tính a, (x+2y)^2 b, (3x-2y)^2 c, (2x-1/2)^2 d, (x/2-y) (x/2+y) e, (x+1/3)^3 d, (x-2) (x^2+2x+4)

Đáp án:

 a, `(x + 2y)^2 = x^2 + 2 . x . 2y + (2y)^2`

 `                      =x^2 + 4xy         +4y²`

b, `(3x – 2y)^2 = (3x)² – 2 . 3x . 2y + (2y)^2`

`                       =9x^2 – 12xy +4y²`

c, `(2x – 1/2)^2 = (2x)^2 – 2 . 2x . 1/2 + (1/2)^2`

                    `    = 4x² – 2x + 1/4`

d, `(x/2 – y)(x/2 + y) = (x/2)^2 – y^2`

                               `=(x²)/4 – y^2`

e, `(x+1/3)^3 = x³ +3 x² . 1/3 + 3x . (1/3)^2 + (1/3)³`

                     `= x³ + x² + 1/3x + 1/27`

f,`(x – 2)(x² + 2x + 4)`

`=(x – 2)(x² + 2x + 2²)`

`=(x – 2)³`