Đáp án+Giải thích các bước giải:

5,

`(x-y)^2+(x+y)^2-2(x+y)(x-y)`

`=(x-y)^2-2(x-y)(x+y)+(x+y)^2`

`=[(x-y)-(x+y)]^2`

`=(x-y-x-y)^2`

`=(-2y)^2`

`=4y^2`

6,

`(5-x)^2+(x+5)^2-(2x+10)(x-5)`

`=(x-5)^2-2.(x-5).(x+5)+(x+5)^2`

`=[(x-5)-(x+5)]^2`

`=(x-5-x-5)^2`

`=(-10)^2`

`=100`

7,

`(x-2)^2+(x+1)^2+2(x-2)(-1-x)`

`=(x-2)^2+2(x-2).(-1)(x+1)+(x+1)^2`

`=(x-2)^2-2(x-2)(x+1)+(x+1)^2`

`=[(x-2)-(x+1)]^2`

`=(x-2-x-1)^2`

`=(-3)^2`

`=9`

8,

`(2x+3y)^2+(2x-3y)^2-2(4x^2-9y^2)`

`=(2x+3y)^2-2(2x+3y)(2x-3y)+(2x-3y)^2`

`=[(2x+3y)-(2x-3y)^2]`

`=(2x+3y-2x+3y)^2`

`=(6y)^2`

`=36y^2`