Đáp án:

 `↓`

Giải thích các bước giải:

`10) (3x+1)^2 -(x+1)^2`

`= [(3x+1)-(x+1)][(3x+1)+(x+1)]`

`=(3x-x+1-1)(3x+x+1+1)`

`=2x.(4x+2)`

`=8x^2 +4x`

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

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

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

`=2y.2x`

`=4xy`

`12) (2xy+1)^2 -(2x+y)^2`

`=[2xy+1-(2x+y)][2xy+1+(2x+y)]`

`=(2xy+1-2x-y)(2xy+1+2x+y)`

`13) 9(x-y)^2 -4(x+y)^2`

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

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

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

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

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

`=(x-5y)(5x-y)`

`= 5x^2 -xy-25xy+5y^2`

`=5x^2 -26xy+5y^2`

`14) (3x-2y)^2 -(2x-3y)^2`

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

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

`=(x+y)(5x-5y)`

`=5x^2 -5xy+5xy-5y^2`

`=5x^2 -5y^2`

`15) (4x^2 -4x+1) -(x+1)^2`

`=[(2x)^2 -2.2x.1+1^2]-(x+1)^2`

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

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

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

`=(x-2).3x`

`=3x^2 -6x`