1.(2x-3y)(2x+3y)=

问题描述:

1.(2x-3y)(2x+3y)=
2.(5x+3y)(3y-5x)
3.(x-3y)(-x+3y)=
4.(x+y-z)²=

1.(2x-3y)(2x+3y)=(2x)²-(3y)²=4x²-9y²
2.(5x+3y)(3y-5x)=(3y)²-(5x)²=9y²-25x²
3.(x-3y)(-x+3y)=-(x-3y)²=-x²+6xy-9y²
4.(x+y-z)²=[(x+y)-z]²
=(x+y)²-2(x+y)z+z²
=x²+2xy+y²-2xz-2yz+z²