Đáp án:

Giải thích các bước giải:

`a.` `9x^2-1=(3x)^2-1=(3x-1)(3x+1)`

`b.` `8x^3+1=(2x)^3+1=(2x+1)[(2x)^2-2x.1+1^2]=(2x+1)(4x^2-2x+1)`

`c.` `(x-1/2)^2=x^2-2 .x  . 1/2+(1/2)^2=x^2-x+1/4`

`d.` `2(x^2+1/2y)(2x^2-y)`

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

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

`=4x^2-y^2`

`e.` `(6x+1/2)(36x^2-3x+1/4)`

`=(6x+1/2)[(6x)^2-6x .1/2+(1/2)^2]`

`=(6x)^3+(1/2)^3`

`=216x^3+1/8`