平方差公式和完全平方公式精讲
- 格式:doc
- 大小:186.50 KB
- 文档页数:8
平方差公式和完全平方公式(讲义)
一、知识点睛
1. 平方差公式:___________________________;
2. 完全平方公式:_________________________;
_________________________. 口诀:首平方、尾平方,乘积二倍在中央.
二、精讲精练
1. 填空:
① (x -4)(x +4)=( )2-( )2=________;
② (3a+2b )(3a -2b )=( )2-( )2=_________________; ③ (-m -n )(m -n )=( )2-( )2=___________________;
④ 11
(2)(2)44
x y x y ---=( )2-( )2=___________;
⑤ (a n +b )(a n -b ) =( )2-( )2=___________________; ⑥ (3a +b +3)(3a +b -3)=( )2-( )2;
⑦ (m +n )(m -n )(m 2+n 2)=( )(m 2+n 2)=( )2 -( )2=_______; ⑧ (x +3y )( )=9y 2-x 2.
2. 下列多项式乘法中,能用平方差公式计算的是( )
A .(x +1)(1+x )
B .(21a +b )(b -2
1
a )
C .(-a +b )(a -b )
D .(x 2-y )(x +y 2) 3. 计算:
(1)(ab +8)(ab -8) (2)(2a -
31b )( -3
1
b -2a )
(3)(2a -b )(2a +b )(4a 2+b 2) (4)(2a +4b )(a -2b )
(5)103×97
(6)20132-2012×2014
① (2x +5y )2=( )2+2( )( )+( )2=__________________;
② 2)2
1
31(-m =( )2-2( )( )+( )2=________________;
③ (-x +y )2=( )2=_________________________________; ④ (-m -n )2=( )2=________________________________; ⑤ (-3x +4y )2=______________________________________;
⑥ 2
)2
14(y x -
-=____________________________________; ⑦ (-xy +2y )2=__________________________________;
⑧ 21
()2
mn m --=___________________________________;
⑨ x 2+4y 2+___=(x -2y )2.
5. 下列各式能够成立的是( ) A .(2a -b )2=4a 2-2ab +b 2
B .(x +y )2=x 2+y 2
C .( -21a -b )2=4
1
a 2+a
b +b 2
D .( -x -y )(x +y )=x 2-y 2
6. 计算:
(1)(-2t -1)2
(2)(m +2n )2-4n 2
(3)(a -b -c )2
(4)1022
7. 若(3x -y )2=a 2x 2-6xy +y 2,则a =_______. 8. 若(ax +y )2=9x 2-6xy +y 2,则a =________.
9. 若4x 2-4xy +my 2是完全平方式,则m =________. 10. 若x 2+axy +9y 2是完全平方式,则a =__________.
11. 多项式4x 2+1加上一个单项式后,能使它成为一个整式的完全平方式,则可
以加上的单项式共有___个,分别是_____
_________________________.
① a 2+b 2=(a +b )2-____________; ② a 2+b 2=(a -b )2+____________; ③ (a +b )2=(a -b )2+___________; ④ (a -b )2=(a +b )2-____________. 13. 若(x +y )2-M =(x -y )2,则M 为( )
A .2xy
B .±2xy
C .4xy
D .±4xy
14. 运用乘法公式计算:
(1)(2x -y )2-4(x +y )(x -y ) (2)(x -2)(x +2)-(x -1)2
(3)(x+2y -3)(x -2y +3)
(4)(a+b -c )(a -b -c )
(5)(a +b )3
(6)22(5)(5)22
x x
+--
(7)1022-982
(8)(n 2+1)2-(n 2-1)2
【参考答案】
一、知识点睛
1.(a+b)(a-b)=a2-b2
2.(a+b)2=a2+2ab+b2 (a-b)2=a2-2ab+b2
二、精讲精练
1.①x 4 x2-16 ②3a2b9a2-4b2
③-n m n2-m2 ④-2y 1
4
x 4y2-
1
16
x2
⑤a n b a2n-b2⑥3a+b3
⑦m2-n2 m2 n2 m4-n4 ⑧3y-x
2. B
3.(1)a2b2-64 (2)1
9
b2-4a2(3)16a4-b4
(4)2a2-8b2 (5)9991 (6)1 4.①2x 2x 5y5y4x2+20xy+25y2
②1
3
m
1
2
1
3
m
1
2
1
9
m2-
1
3
m+
1
4
③y-x y2-2xy+ x2④m+n m2 +2mn+n2
⑤ 9x2-24xy+16y2 ⑥ 16x2+4xy+1
4
y2
⑦x2y2-4xy2+4y2 ⑧m2n2+ m2n+1
4
m2
⑨(-4xy)
5.C
6.①4t2+4t+1 ②m2+4mn ③a2+b2 +c2+2bc-2ac-2ab
④10404
7.±38.-3 9.1 10.±6
11.5 -1-4x2-4x4x4x4
12.①2ab ②2ab ③4ab ④4ab
13.C
14.(1)5y2-4xy (2)2x-5 (3)x2-4y2+12y-9 (4)a2-b2 +c2 -2ac (5)a3+b3 +3a2b +3ab2
(6)10x (7)800 (8)4n2