初等数论总结
初等数论
一、整除
1. 定义
设 a , b ∈ Z , a ≠ 0 a, b \in Z, a \neq 0 a,b∈Z,a=0 ,若 ∃ q ∈ Z \exist q \in Z ∃q∈Z ,使得 b = a q b = aq b=aq ,则有 b b b 能被 a a a 整除,记作 a ∣ b a \mid b a∣b ,且称 b b b 是 a a a 的因数, a a a 是 b b b 的约数,反之即 b b b 不能被 a a a 整除,则记为 a ∤ b a \nmid b a∤b ;
2. 性质
性质1
若 a ∣ b a \mid b a∣b 且 b ∣ c b \mid c b∣c ,则 a ∣ c a \mid c a∣c ;
证明如下,
∵ a ∣ b 则令 a x = b ( x ∈ Z 且 x ≠ 0 ) b ∣ c 则令 b y = c ( y ∈ Z 且 y ≠ 0 ) ∴ a x y = c ( x , y ∈ Z 且 x , y ≠ 0 ) ∴ a ∣ c \begin{aligned} & \because a \mid b \; 则令 \; ax = b (x \in Z \; 且 \; x \neq 0) \\ & \quad \; b \mid c \; 则令 \; by = c (y \in Z \; 且 \; y \neq 0) \\ & \therefore axy = c (x, y \in Z \; 且 \; x, y \neq 0) \\ & \therefore a \mid c \end{aligned} ∵a∣b则令ax=b(x∈Z且x=0)b∣c则令by=c(y∈Z且y=0)∴axy=c(x,y∈Z且x,y=0)∴a∣c
性质2
a ∣ b a \mid b a∣b 且 a ∣ c a \mid c a∣c 等价于对 ∀ Z x , y \forall Z x, y ∀Zx,y ,有 a ∣ ( b x + c y ) a \mid (bx + cy) a∣(bx+cy) ;
证明如下,
∵ a ∣ b 则令 a p = b ( p ∈ Z 且 p ≠ 0 ) a ∣ c 则令 a q = c ( q ∈ Z 且 q ≠ 0 ) 又 ∵ b x + c y = a p x + a q y = a ( p x + q y ) 又 ∵ a ∣ ( a ( p x + q y ) ) ∴ a ∣ ( b x + c y ) \begin{aligned} & \because a \mid b \; 则令 \; ap = b (p \in Z \; 且 \; p \neq 0) \\ & \quad \; a \mid c \; 则令 \; aq = c (q \in Z \; 且 \; q \neq 0) \\ & 又\because bx + cy = apx + aqy = a(px + qy) \\ & 又\because a \mid (a(px + qy)) \\ & \therefore a \mid (bx + cy) \end{aligned} ∵a∣b则令ap=b(p∈Z且p=0)a∣c则令aq=c(q∈Z且q=0)又∵bx+cy=apx+aqy=a(px+qy)又∵a∣(a(px+qy))∴a∣(bx+cy)
性质3
设 m ≠ 0 m \neq 0 m=0 ,则 a ∣ b a \mid b a∣b 等价于 ( m a ) ∣ ( m b ) (ma) \mid (mb) (ma)∣(mb) ;
证明如下,
∵ a ∣ b 则令 a q = b ( p ∈ Z 且 p ≠ 0 ) ∴ a q m = b m ∴ ( m a ) ∣ ( m b ) \begin{aligned} & \because a \mid b \; 则令 \; aq = b (p \in Z \; 且 \; p \neq 0) \\ & \therefore aqm = bm \\ & \therefore (ma) \mid (mb) \end{aligned} ∵a∣b则令aq=b(p∈Z且p=0)∴aqm=bm∴(ma)∣(mb)
性质4
设有 x , y ∈ Z x, y \in Z x,y∈Z 满足 a x + b y = 1 ax + by = 1 ax+by=1 ,且 a ∣ n , b ∣ n a \mid n, b \mid n a∣n,b∣n ,则 ( a b ) ∣ n (ab) \mid n (ab)∣n ;
证明如下,
∵ a ∣ n , b ∣ n ∴ ( a b ) ∣ ( n b ) , ( a b ) ∣ ( n a ) ∴ ( a b ) ∣ ( n b y + n a x ) ∴ ( a b ) ∣ ( n ( b y + a x ) ) ∴ ( a b ) ∣ n \begin{aligned} & \because a \mid n, b \mid n \\ & \therefore (ab) \mid (nb), (ab) \mid (na) \\ & \therefore (ab) \mid (nby + nax) \\ & \therefore (ab) \mid (n(by + ax)) \\ & \therefore (ab) \mid n \\ \end{aligned} ∵a∣n,b∣n∴(ab)∣(nb),(ab)∣(na)∴(ab)∣(nby+nax)∴(ab)∣(n(by+ax))∴(ab)∣n
性质5
若 b = q d + c , q ∈ Z b = qd + c, q \in Z b=qd+c,q∈Z ,则 d ∣ b d \mid b d∣b 的充分必要条件为 d ∣ c d \mid c d∣c ;
证明如下,
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证明必要性,即 b = q d + c , q ∈ Z b = qd + c, q \in Z b=qd+c,q∈Z 且 d ∣ b d \mid b d∣b 可得 d ∣ c d \mid c d∣c ;
∵ d ∣ b 则令 d x = b ( x ∈ Z 且 x ≠ 0 ) ∴ d x = q d + c ∴ d ( x − q ) = c ∴ d ∣ c \begin{aligned} & \because d \mid b \; 则令 \; dx = b (x \in Z \; 且 \; x \neq 0) \\ & \therefore dx = qd + c \\ & \therefore d(x - q) = c \\ & \therefore d \mid c \end{aligned} ∵d∣b则令dx=b(x∈Z且x=0)∴dx=qd+c∴d(x−q)=c∴d∣c
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证明充分性,即 b = q d + c , q ∈ Z b = qd + c, q \in Z b=qd+c,q∈Z 且 d ∣ c d \mid c d∣c 可得 d ∣ b d \mid b d∣b ;
∵ d ∣ c 则令 d x = c ( x ∈ Z 且 x ≠ 0 ) ∴ b = q d + x d ∴ d ( x + q ) = b ∴ d ∣ b \begin{aligned} & \because d \mid c \; 则令 \; dx = c (x \in Z \; 且 \; x \neq 0) \\ & \therefore b = qd + xd \\ & \therefore d(x + q) = b \\ & \therefore d \mid b \end{aligned} ∵d∣c则令dx=c(x∈Z且x=0)∴b=qd+xd∴d(x+q)=b∴d∣b
二、模运算
1. 定义
对于 a , b ∈ Z , b ≠ 0 a, b \in Z, b \neq 0 a,b∈Z,b=0 , a ÷ b a \div b a÷b 的余数即为 a a a 模 b b b ,记作 a m o d b a \; mod \; b amodb ;
2. 性质
分配律
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加法, ( a + b ) m o d c = ( a m o d c + b m o d c ) m o d c (a + b) \; mod \; c = (a \; mod \; c + b \; mod \; c) \; mod \; c (a+b)modc=(amodc+bmodc)modc ;
证明如下,
设 a = c p + x ( p , x ∈ Z , 0 ≤ x < c ) b = c q + y ( q , y ∈ Z , 0 ≤ y < c ) ∴ ( a + b ) m o d c = ( c ( p + q ) + x + y ) m o d c = ( x + y ) m o d c ∴ ( a + b ) m o d c = ( a m o d c + b m o d c ) m o d c \begin{aligned} & 设 a = cp + x (p, x \in Z, 0 \leq x < c) \\ & \quad b = cq + y (q, y \in Z, 0 \leq y < c) \\ & \therefore (a + b) \; mod \; c = (c(p + q) + x + y) \; mod \; c = (x + y) \; mod \; c \\ & \therefore (a + b) \; mod \; c = (a \; mod \; c + b \; mod \; c) \; mod \; c \end{aligned} 设a=cp+x(p,x∈Z,0≤x<c)b=cq+y(q,y∈Z,0≤y<c)∴(a+b)modc=(c(p+q)+x+y)modc=(x+y)modc∴(a+b)modc=(amodc+bmodc)modc
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减法, ( a − b ) m o d c = ( a m o d c − b m o d c ) m o d c (a - b) \; mod \; c = (a \; mod \; c - b \; mod \; c) \; mod \; c (a−b)modc=(amodc−bmodc)modc ;
证明如下,
设 a = c p + x ( p , x ∈ Z , 0 ≤ x < c ) b = c q + y ( q , y ∈ Z , 0 ≤ y < c ) ∴ ( a − b ) m o d c = ( c ( p − q ) + x − y ) m o d c = ( x − y ) m o d c ∴ ( a − b ) m o d c = ( a m o d c − b m o d c ) m o d c \begin{aligned} & 设 a = cp + x (p, x \in Z, 0 \leq x < c) \\ & \quad b = cq + y (q, y \in Z, 0 \leq y < c) \\ & \therefore (a - b) \; mod \; c = (c(p - q) + x - y) \; mod \; c = (x - y) \; mod \; c \\ & \therefore (a - b) \; mod \; c = (a \; mod \; c - b \; mod \; c) \; mod \; c \end{aligned} 设a=cp+x(p,x∈Z,0≤x<c)b=cq+y(q,y∈Z,0≤y<c)∴(a−b)modc=(c(p−q)+x−y)modc=(x−y)modc∴(a−b)modc=(amodc−bmodc)modc
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乘法, ( a b ) m o d c = ( a m o d c × b m o d c ) m o d c (ab) \; mod \; c = (a \; mod \; c \times b \; mod \; c) \; mod \; c (ab)modc=(amodc×bmodc)modc ;
证明如下,
设 a = c p + x ( p , x ∈ Z , 0 ≤ x < c ) b = c q + y ( q , y ∈ Z , 0 ≤ y < c ) ( a b ) m o d c = ( ( c p + x ) ∗ ( c q + y ) ) m o d c = ( c c p q + c p y + c q x + x y ) m o d c = x y m o d c = ( a m o d c × b m o d c ) m o d c \begin{aligned} & 设 a = cp + x (p, x \in Z, 0 \leq x < c) \\ & \quad b = cq + y (q, y \in Z, 0 \leq y < c) \\ & \quad \; (ab) \; mod \; c \\ & = ((cp + x) * (cq + y)) \; mod \; c \\ & = (ccpq + cpy + cqx + xy) \; mod \; c \\ & = xy \; mod \; c \\ & = (a \; mod \; c \times b \; mod \; c) \; mod \; c \end{aligned} 设a=cp+x(p,x∈Z,0≤x<c)b=cq+y(q,y∈Z,0≤y<c)(ab)modc=((cp+x)∗(cq+y))modc=(ccpq+cpy+cqx+xy)modc=xymodc=(amodc×bmodc)modc
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扩展, ( a b ) m o d c = ( a m o d c ) b m o d c (a^b) \; mod \; c = (a \; mod \; c)^b \; mod \; c (ab)modc=(amodc)bmodc ;
放缩性
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乘法,有 a m o d b = c , d ≠ 0 a \; mod \; b = c, d \neq 0 amodb=c,d=0 ,则有 ( a d ) m o d ( b d ) = c d (ad) \; mod \; (bd) = cd (ad)mod(bd)=cd ;
证明如下,
∵ a m o d b = c 则令 a = b x + c ( x ∈ Z ) ∴ a d = b d x + c d ∴ ( b d x + c d ) m o d ( b d ) = c d ∴ ( a d ) m o d ( b d ) = c d \begin{aligned} & \because a \; mod \; b = c \; 则令 \; a = bx + c (x \in Z) \\ & \therefore ad = bdx + cd \\ & \therefore (bdx + cd) \; mod \; (bd) = cd \\ & \therefore (ad) \; mod \; (bd) = cd \end{aligned} ∵amodb=c则令a=bx+c(x∈Z)∴ad=bdx+cd∴(bdx+cd)mod(bd)=cd∴(ad)mod(bd)=cd
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除法,有 a m o d b = c , d ≠ 0 a \; mod \; b = c, d \neq 0 amodb=c,d=0 ,则有 ( a d ) m o d ( b d ) = c d (\frac{a}{d}) \; mod \; (\frac{b}{d}) = \frac{c}{d} (da)mod(db)=dc ;
3. 推论
推论1
若 2 能整除 a a a 的最末位 (0 能被 ∀ Z \forall Z ∀Z 整除) ,则 a a a 能被 2 整除;
证明如下,
设 a = 10 x + y ( x , y ∈ Z + , 0 ≤ y ≤ 9 ) ∴ 2 ∣ y 又 ∵ a m o d 2 = ( 10 x m o d 2 + y m o d 2 ) m o d 2 = 0 ∴ 2 ∣ a \begin{aligned} & 设 \; a = 10x + y (x, y \in Z^{+}, 0 \leq y \leq 9) \\ & \therefore 2 \mid y \\ & 又\because a \; mod \; 2 = (10x \; mod \; 2 + y \; mod \; 2) \; mod \; 2 = 0 \\ & \therefore 2 \mid a \end{aligned} 设a=10x+y(x,y∈Z+,0≤y≤9)∴2∣y又∵amod2=(10xmod2+ymod2)mod2=0∴2∣a
推论2
若 4 能整除 a a a 的最末 2 位 (0 能被 ∀ Z \forall Z ∀Z 整除) ,则 a a a 能被 4 整除;
证明如下,
设 a = 100 x + y ( x , y ∈ Z + , 0 ≤ y ≤ 99 ) ∴ 4 ∣ y 又 ∵ a m o d 4 = ( 100 x m o d 4 + y m o d 4 ) m o d 4 = 0 ∴ 4 ∣ a \begin{aligned} & 设 \; a = 100x + y (x, y \in Z^{+}, 0 \leq y \leq 99) \\ & \therefore 4 \mid y \\ & 又\because a \; mod \; 4 = (100x \; mod \; 4 + y \; mod \; 4) \; mod \; 4 = 0 \\ & \therefore 4 \mid a \end{aligned} 设a=100x+y(x,y∈Z+,0≤y≤99)∴4∣y又∵amod4=(100xmod4+ymod4)mod4=0∴4∣a
推论3
若 8 能整除 a a a 的最末 3 位 (0 能被 ∀ Z \forall Z ∀Z 整除) ,则 a a a 能被 8 整除;
证明如下,
设 a = 1000 x + y ( x , y ∈ Z + , 0 ≤ y ≤ 999 ) ∴ 8 ∣ y 又 ∵ a m o d 8 = ( 1000 x m o d 8 + y m o d 8 ) m o d 8 = 0 ∴ 8 ∣ a \begin{aligned} & 设 \; a = 1000x + y (x, y \in Z^{+}, 0 \leq y \leq 999) \\ & \therefore 8 \mid y \\ & 又\because a \; mod \; 8 = (1000x \; mod \; 8 + y \; mod \; 8) \; mod \; 8 = 0 \\ & \therefore 8 \mid a \end{aligned} 设a=1000x+y(x,y∈Z+,0≤y≤999)∴8∣y又∵amod8=(1000xmod8+ymod8)mod8=0∴8∣a
推论4
若 3 能整除 a a a 的各个数位之和,则 a a a 能被 3 整除;
证明如下,以 3 位数为例,
设 a = x y z ‾ ( x , y , z ∈ Z + , 1 ≤ x ≤ 9 , 0 ≤ y , z ≤ 9 ) ∴ ( x + y + z ) m o d 3 = 0 ∴ x y z ‾ m o d 3 = ( 100 x + 10 y + z ) m o d 3 = 100 x m o d 3 + 10 y m o d 3 + z m o d 3 = x m o d 3 + y m o d 3 + z m o d 3 = 0 ∴ 3 ∣ a \begin{aligned} & 设 \; a = \overline{xyz} \; (x, y, z \in Z^{+}, 1 \leq x \leq 9, 0 \leq y,z \leq 9) \\ & \therefore (x + y + z) \; mod \; 3 = 0 \\ & \therefore \overline{xyz} \; mod \; 3 \\ & = (100x + 10 y + z) \; mod \; 3 \\ & = 100x \; mod \; 3 + 10y \; mod \; 3 + z \; mod \; 3 \\ & = x \; mod \; 3 + y \; mod \; 3 + z \; mod \; 3 \\ & = 0 \\ & \therefore 3 \mid a \end{aligned} 设a=xyz(x,y,z∈Z+,1≤x≤9,0≤y,z≤9)∴(x+y+z)mod3=0∴xyzmod3=(100x+10y+z)mod3=100xmod3+10ymod3+zmod3=xmod3+ymod3+zmod3=0∴3∣a
推论5
若 9 能整除 a a a 的各个数位之和,则 a a a 能被 9 整除;
证明如下,以 3 位数为例,
设 a = x y z ‾ ( x , y , z ∈ Z + , 1 ≤ x ≤ 9 , 0 ≤ y , z ≤ 9 ) ∴ ( x + y + z ) m o d 9 = 0 ∴ x y z ‾ m o d 9 = ( 100 x + 10 y + z ) m o d 9 = 100 x m o d 9 + 10 y m o d 9 + z m o d 9 = x m o d 9 + y m o d 9 + z m o d 9 = 0 ∴ 9 ∣ a \begin{aligned} & 设 \; a = \overline{xyz} \; (x, y, z \in Z^{+}, 1 \leq x \leq 9, 0 \leq y,z \leq 9) \\ & \therefore (x + y + z) \; mod \; 9 = 0 \\ & \therefore \overline{xyz} \; mod \; 9 \\ & = (100x + 10 y + z) \; mod \; 9 \\ & = 100x \; mod \; 9 + 10y \; mod \; 9 + z \; mod \; 9 \\ & = x \; mod \; 9 + y \; mod \; 9 + z \; mod \; 9 \\ & = 0 \\ & \therefore 9 \mid a \end{aligned} 设a=xyz(x,y,z∈Z+,1≤x≤9,0≤y,z≤9)∴(x+y+z)mod9=0∴xyzmod9=(100x+10y+z)mod9=100xmod9+10ymod9+zmod9=xmod9+ymod9+zmod9=0∴9∣a
推论6
若 11 能整除 a a a 的奇数数位与偶数数位的差,则 a a a 能被 11 整除;
证明如下,以 5 位数为例,
设 a = x 1 x 2 x 3 x 4 x 5 ‾ ( x 1 , x 2 , x 3 , x 4 , x 5 ∈ Z + , 1 ≤ x 1 ≤ 9 , 0 ≤ x 2 , x 3 , x 4 , x 5 ≤ 9 ) ∴ ( x 1 + x 3 + x 5 − x 2 − x 4 ) m o d 11 = 0 ∴ x 1 x 2 x 3 x 4 x 5 ‾ m o d 11 = ( ( 9999 + 1 ) x 1 + ( 1001 − 1 ) x 2 + ( 99 + 1 ) x 3 + ( 11 − 1 ) x 4 + x 5 ) m o d 11 = ( x 1 − x 2 + x 3 − x 4 + x 5 ) m o d 11 = 0 ∴ 11 ∣ a \begin{aligned} & 设 \; a = \overline{x_1x_2x_3x_4x_5} \; (x_1, x_2, x_3, x_4, x_5 \in Z^{+}, 1 \leq x_1 \leq 9, 0 \leq x_2, x_3, x_4, x_5 \leq 9) \\ & \therefore (x_1 + x_3 + x_5 - x_2 - x_4) \; mod \; 11 = 0 \\ & \therefore \overline{x_1x_2x_3x_4x_5} \; mod \; 11 \\ & = ((9999 + 1)x_1 + (1001 - 1)x_2 + (99 + 1)x_3 + (11 - 1)x_4 + x_5) \; mod \; 11 \\ & = (x_1 - x_2 + x_3 - x_4 + x_5) \; mod \; 11 \\ & = 0 \\ & \therefore 11 \mid a \end{aligned} 设a=x1x2x3x4x5(x1,x2,x3,x4,x5∈Z+,1≤x1≤9,0≤x2,x3,x4,x5≤9)∴(x1+x3+x5−x2−x4)mod11=0∴x1x2x3x4x5mod11=((9999+1)x1+(1001−1)x2+(99+1)x3+(11−1)x4+x5)mod11=(x1−x2+x3−x4+x5)mod11=0∴11∣a
推论7
若 7, 11, 13 能整除 a a a 的末 3 位与末 3 位以前的数字所组成的数的差,则 a a a 能被 7, 11, 13 整除;
证明如下,以 5 位数为例,
设 a = x 1 x 2 x 3 x 4 x 5 ‾ ( x 1 , x 2 , x 3 , x 4 , x 5 ∈ Z + , 1 ≤ x 1 ≤ 9 , 0 ≤ x 2 , x 3 , x 4 , x 5 ≤ 9 ) ∴ x 3 x 4 x 5 ‾ − x 1 x 2 ‾ m o d 1001 = 0 ∴ x 1 x 2 x 3 x 4 x 5 ‾ m o d 1001 = ( x 1 x 2 ‾ ∗ 1000 + x 3 x 4 x 5 ‾ ) m o d 1001 = ( − x 1 x 2 ‾ + x 3 x 4 x 5 ‾ ) m o d 1001 = 0 ∴ 1001 ∣ a \begin{aligned} & 设 \; a = \overline{x_1x_2x_3x_4x_5} \; (x_1, x_2, x_3, x_4, x_5 \in Z^{+}, 1 \leq x_1 \leq 9, 0 \leq x_2, x_3, x_4, x_5 \leq 9) \\ & \therefore \overline{x_3x_4x_5} - \overline{x_1x_2} \; mod \; 1001 = 0 \\ & \therefore \overline{x_1x_2x_3x_4x_5} \; mod \; 1001 \\ & = (\overline{x_1x_2} * 1000 + \overline{x_3x_4x_5}) \; mod \; 1001 \\ & = (-\overline{x_1x_2} + \overline{x_3x_4x_5}) \; mod \; 1001 \\ & = 0 \\ & \therefore 1001 \mid a \end{aligned} 设a=x1x2x3x4x5(x1,x2,x3,x4,x5∈Z+,1≤x1≤9,0≤x2,x3,x4,x5≤9)∴x3x4x5−x1x2mod1001=0∴x1x2x3x4x5mod1001=(x1x2∗1000+x3x4x5)mod1001=(−x1x2+x3x4x5)mod1001=0∴1001∣a
三、同余
1. 定义
若 a , b ∈ Z , m ∈ Z + a, b \in Z,m \in Z^{+} a,b∈Z,m∈Z+ ,且 m ∣ ( a − b ) m \mid (a - b) m∣(a−b) ,或 a = b + k m ( k ∈ Z ) a = b + km (k \in Z) a=b+km(k∈Z) 则称 a a a 与 b b b 模 m m m 同余,记为 a ≡ b ( m o d m ) a \equiv b (mod \; m) a≡b(modm) ;
证明 m ∣ ( a − b ) ⇔ a ≡ b ( m o d m ) m \mid (a - b) \Leftrightarrow a \equiv b (mod \; m) m∣(a−b)⇔a≡b(modm) 如下,
∵ m ∣ ( a − b ) ∴ m ( q 1 − q 2 ) = a − b ( q 1 , q 2 ∈ Z ) ∴ a − m q 1 = b − m p 2 = r ∴ a = m q 1 + r , b = m p 2 + r ∴ a ≡ b ( m o d m ) \begin{aligned} & \because m \mid (a - b) \\ & \therefore m(q_1 - q_2) = a - b (q_1, q_2 \in Z) \\ & \therefore a - mq_1 = b - mp_2 = r \\ & \therefore a = mq_1 + r, b = mp_2 + r \\ & \therefore a \equiv b (mod \; m) \\ \end{aligned} ∵m∣(a−b)∴m(q1−q2)=a−b(q1,q2∈Z)∴a−mq1=b−mp2=r∴a=mq1+r,b=mp2+r∴a≡b(modm)
2. 性质
自反性
a ≡ a ( m o d m ) a \equiv a (mod \; m) a≡a(modm) ;
证明如下,
∵ m ∣ ( a − a ) ∴ a ≡ a ( m o d m ) \begin{aligned} & \because m \mid (a - a) \\ & \therefore a \equiv a (mod \; m) \end{aligned} ∵m∣(a−a)∴a≡a(modm)
对称性
a ≡ b ( m o d m ) a \equiv b (mod \; m) a≡b(modm) 则 b ≡ a ( m o d m ) b \equiv a (mod \; m) b≡a(modm) ;
证明如下,
∵ a ≡ b ( m o d m ) ∴ m ∣ ( a − b ) ∴ m ∣ ( b − a ) ∴ b ≡ a ( m o d m ) \begin{aligned} & \because a \equiv b (mod \; m) \\ & \therefore m \mid (a - b) \\ & \therefore m \mid (b - a) \\ & \therefore b \equiv a (mod \; m) \end{aligned} ∵a≡b(modm)∴m∣(a−b)∴m∣(b−a)∴b≡a(modm)
传递性
若 a ≡ b ( m o d m ) a \equiv b (mod \; m) a≡b(modm) 且 b ≡ c ( m o d m ) b \equiv c (mod \; m) b≡c(modm) ,则 a ≡ c ( m o d m ) a \equiv c (mod \; m) a≡c(modm) ;
证明如下,
∵ m ∣ ( a − b ) , m ∣ ( b − c ) ∴ m ∣ ( a − b + b − c ) ∴ m ∣ ( a − c ) ∴ a ≡ c ( m o d m ) \begin{aligned} & \because m \mid (a - b), m \mid (b - c) \\ & \therefore m \mid (a - b + b - c) \\ & \therefore m \mid (a - c) \\ & \therefore a \equiv c (mod \; m) \end{aligned} ∵m∣(a−b),m∣(b−c)∴m∣(a−b+b−c)∴m∣(a−c)∴a≡c(modm)
同加性
若 a ≡ b ( m o d m ) a \equiv b (mod \; m) a≡b(modm) ,则 a + c ≡ b + c ( m o d m ) a + c \equiv b + c (mod \; m) a+c≡b+c(modm) ;
证明如下,
∵ a ≡ b ( m o d m ) ∴ m ∣ ( a − b ) ∴ m ∣ ( a − b ) + c − c ∴ m ∣ ( a + c ) − ( b + c ) ∴ a + c ≡ b + c ( m o d m ) \begin{aligned} & \because a \equiv b (mod \; m) \\ & \therefore m \mid (a - b) \\ & \therefore m \mid (a - b) + c - c \\ & \therefore m \mid (a + c) - (b + c) \\ & \therefore a + c \equiv b + c (mod \; m) \end{aligned} ∵a≡b(modm)∴m∣(a−b)∴m∣(a−b)+c−c∴m∣(a+c)−(b+c)∴a+c≡b+c(modm)
同减性
若 a ≡ b ( m o d m ) a \equiv b (mod \; m) a≡b(modm) ,则 a − c ≡ b − c ( m o d m ) a - c \equiv b - c (mod \; m) a−c≡b−c(modm) ;
证明如下,
∵ a ≡ b ( m o d m ) ∴ m ∣ ( a − b ) ∴ m ∣ ( a − b ) − c + c ∴ m ∣ ( a − c ) − ( b − c ) ∴ a − c ≡ b − c ( m o d m ) \begin{aligned} & \because a \equiv b (mod \; m) \\ & \therefore m \mid (a - b) \\ & \therefore m \mid (a - b) - c + c \\ & \therefore m \mid (a - c) - (b - c) \\ & \therefore a - c \equiv b - c (mod \; m) \end{aligned} ∵a≡b(modm)∴m∣(a−b)∴m∣(a−b)−c+c∴m∣(a−c)−(b−c)∴a−c≡b−c(modm)
同乘性
若 a ≡ b ( m o d m ) a \equiv b (mod \; m) a≡b(modm) ,则 a c ≡ b c ( m o d m ) ac \equiv bc (mod \; m) ac≡bc(modm) ;
证明如下,
∵ a ≡ b ( m o d m ) ∴ m ∣ ( a − b ) ∴ m ∣ c ( a − b ) ∴ m ∣ c a − c b ∴ a c ≡ b c ( m o d m ) \begin{aligned} & \because a \equiv b (mod \; m) \\ & \therefore m \mid (a - b) \\ & \therefore m \mid c(a - b) \\ & \therefore m \mid ca - cb \\ & \therefore ac \equiv bc (mod \; m) \end{aligned} ∵a≡b(modm)∴m∣(a−b)∴m∣c(a−b)∴m∣ca−cb∴ac≡bc(modm)
同除性
若 a ≡ b ( m o d m ) a \equiv b (mod \; m) a≡b(modm) 且 c ∣ a , c ∣ b , ( c , m ) = 1 c \mid a, c \mid b, (c, m) = 1 c∣a,c∣b,(c,m)=1 ,则 a c ≡ b c ( m o d m ) \frac ac \equiv \frac bc (mod \; m) ca≡cb(modm) ;
∵ a ≡ b ( m o d m ) ∴ m ∣ ( a − b ) 又 ∵ ( c , m ) = 1 ∴ m ∣ ( a − b ) c ∴ m ∣ a c − b c ∴ a c ≡ b c ( m o d m ) \begin{aligned} & \because a \equiv b (mod \; m) \\ & \therefore m \mid (a - b) \\ & 又\because (c, m) = 1 \\ & \therefore m \mid \frac{(a - b)}{c} \\ & \therefore m \mid \frac ac - \frac bc \\ & \therefore \frac ac \equiv \frac bc (mod \; m) \end{aligned} ∵a≡b(modm)∴m∣(a−b)又∵(c,m)=1∴m∣c(a−b)∴m∣ca−cb∴ca≡cb(modm)
同幂性
若 a ≡ b ( m o d m ) a \equiv b (mod \; m) a≡b(modm) ,则 a n ≡ b n ( m o d m ) a^n \equiv b^n (mod \; m) an≡bn(modm) ;
证明如下,
∵ a ≡ b ( m o d m ) ∴ a m o d m = b m o d m ∴ ( a m o d m ) n = ( b m o d m ) n ∴ ( a m o d m ) n − ( b m o d m ) n = 0 ∴ a n ≡ b n ( m o d m ) \begin{aligned} & \because a \equiv b (mod \; m) \\ & \therefore a \; mod \; m = b \; mod \; m \\ & \therefore (a \; mod \; m)^n = (b \; mod \; m)^n \\ & \therefore (a \; mod \; m)^n - (b \; mod \; m)^n = 0 \\ & \therefore a^n \equiv b^n (mod \; m) \end{aligned} ∵a≡b(modm)∴amodm=bmodm∴(amodm)n=(bmodm)n∴(amodm)n−(bmodm)n=0∴an≡bn(modm)
推论1
若 a ≡ b ( m o d m ) , c ≡ d ( m o d m ) a \equiv b (mod \; m), c \equiv d (mod \; m) a≡b(modm),c≡d(modm) ,则 a + b ≡ c + d ( m o d m ) a + b \equiv c + d (mod \; m) a+b≡c+d(modm) ;
证明如下,
∵ a ≡ b ( m o d m ) ∴ m ∣ ( a − b ) ∵ c ≡ d ( m o d m ) ∴ m ∣ ( c − d ) ∴ m ∣ ( a − b + c − d ) ∴ a + b ≡ c + d ( m o d m ) \begin{aligned} & \because a \equiv b (mod \; m) \\ & \therefore m \mid (a - b) \\ & \because c \equiv d (mod \; m) \\ & \therefore m \mid (c - d) \\ & \therefore m \mid (a - b + c - d) \\ & \therefore a + b \equiv c + d (mod \; m) \end{aligned} ∵a≡b(modm)∴m∣(a−b)∵c≡d(modm)∴m∣(c−d)∴m∣(a−b+c−d)∴a+b≡c+d(modm)
推论2
若 a ≡ b ( m o d m ) , c ≡ d ( m o d m ) a \equiv b (mod \; m), c \equiv d (mod \; m) a≡b(modm),c≡d(modm) ,则 a b ≡ c d ( m o d m ) ab \equiv cd (mod \; m) ab≡cd(modm) ;
证明如下,
∵ a ≡ b ( m o d m ) ∴ m ∣ c ( a − b ) ∵ c ≡ d ( m o d m ) ∴ m ∣ a ( c − d ) ∴ m ∣ ( a c − b c + b c − c d ) ∴ a b ≡ c d ( m o d m ) \begin{aligned} & \because a \equiv b (mod \; m) \\ & \therefore m \mid c(a - b) \\ & \because c \equiv d (mod \; m) \\ & \therefore m \mid a(c - d) \\ & \therefore m \mid (ac - bc + bc - cd) \\ & \therefore ab \equiv cd (mod \; m) \end{aligned} ∵a≡b(modm)∴m∣c(a−b)∵c≡d(modm)∴m∣a(c−d)∴m∣(ac−bc+bc−cd)∴ab≡cd(modm)
推论3
若 a m o d p = x , a m o d q = x , ( p , q ) = 1 a \; mod \; p = x, a \; mod \; q = x, (p, q) = 1 amodp=x,amodq=x,(p,q)=1 ,则 a m o d ( p q ) = x a \; mod \; (pq) = x amod(pq)=x ;
证明如下,
∵ a m o d p = x 则令 s p = a − x a m o d q = x 则令 t q = a − x ∴ s p = t q ∵ ( p , q ) = 1 ∴ s = n q ∴ a = n p q + x ∴ a m o d ( p q ) = x \begin{aligned} & \because a \; mod \; p = x \; 则令 \; sp = a - x \\ & \quad \; a \; mod \; q = x \; 则令 \; tq = a - x \\ & \therefore sp = tq \\ & \because (p, q) = 1 \\ & \therefore s = nq \\ & \therefore a = npq + x \\ & \therefore a \; mod \; (pq) = x \end{aligned} ∵amodp=x则令sp=a−xamodq=x则令tq=a−x∴sp=tq∵(p,q)=1∴s=nq∴a=npq+x∴amod(pq)=x