Question

数学 七年级 下册

平方差公式
（a+2)(a-2)=
(3a+2b)(3a-2b)=
(-x+1)(-x-1)=
(-4k+3)(-4k-3)=
(3x+7y)(3x-7y)=
(0.2x-0.3)(0.2x+0.3)=
(mn-3n)(mn+3n)=
(-2x+3y)(-2x-3y)=
(-1/4x-2y)(-1/4x+2y)=
x²+(y-x)(y+x)=
要过程

Answer 1

解：
(a+2)(a-2)=a²-2²=a²-4
(3a+2b)(3a-2b)=(3a)²-(2b)²=9a²-4b²
(-x+1)(-x-1)=(-x)²-1²=x²-1
(-4k+3)(-4k-3)=(-4k)²-3²=16k²-9
(3x+7y)(3x-7y)=(3x)²-(7y)²=9x²-49y²
(0.2x-0.3)(0.2x+0.3)=(0.2x)²-(0.3)²=0.04x²-0.09
(mn-3n)(mn+3n)=(mn)²-(3n)²=m²n²-9n²
(-2x+3y)(-2x-3y)=(-2x)²-(3y)²=4x²-9y²
(-1/4x-2y)(-1/4x+2y)=(-1/4x)²-(2y)²=1/16x²-4y²
x²+(y-x)(y+x)=x²+(y²-x²)=x²+y²-x²=y²

Answer 2

（a+2)(a-2)=a²-4
(3a+2b)(3a-2b)=9a²-4b²
(-x+1)(-x-1)=x²-1
(-4k+3)(-4k-3)=16k²-9
(3x+7y)(3x-7y)=9x²-49y²
(0.2x-0.3)(0.2x+0.3)=0.04x²-0.09
(mn-3n)(mn+3n)=m²n²-9n²
(-2x+3y)(-2x-3y)=4x²-9y²
(-1/4x-2y)(-1/4x+2y)=1/16x²-4y²
x²+(y-x)(y+x)=x²+y²-x²=y²

Answer 3

这么简单，不是有定理的么这个都不知道啊
（a+2)(a-2)=a²-4

(3a+2b)(3a-2b)=9a²-4b²

(-x+1)(-x-1)=x²-1

(-4k+3)(-4k-3)=16k²-9

(3x+7y)(3x-7y)=9x²-49y²

(0.2x-0.3)(0.2x+0.3)=0.04x²-0.09

(mn-3n)(mn+3n)=m²n²-9n²

(-2x+3y)(-2x-3y)=4x²-9y²

(-1/4x-2y)(-1/4x+2y)=1/16x²-4y²

x²+(y-x)(y+x)=x²+y²-x²=y²

Answer 4

[a+2)(a-2)=a²-2²=a²-4
(3a+2b)(3a-2b)=(3a)²-(2b)²=9a²-4b²
(-x+1)(-x-1)=(-x)²-1²=x²-1
(-4k+3)(-4k-3)=(-4k)²-3²=16k²-9
(3x+7y)(3x-7y)=(3x)²-(7y)²=9x²-49y²
(0.2x-0.3)(0.2x+0.3)=(0.2x)²-(0.3)²=0.04x²-0.09
(mn-3n)(mn+3n)=(mn)²-(3n)²=m²n²-9n²
(-2x+3y)(-2x-3y)=(-2x)²-(3y)²=4x²-9y²
(-1/4x-2y)(-1/4x+2y)=(-1/4x)²-(2y)²=1/16x²-4y²
x²+(y-x)(y+x)=x²+(y²-x²)=x²+y²-x²=y² 应该是这样吧..