a) 5x(x^2-3xy+4y) b) (2x+3)(x-2) c) (4x-5)(x+2)-3x(x+4) d) (2x-1/2)^2-(x-1/3)(3x-3/4)

Đáp án:

a. `5x^3 -15x^2 y+20xy`

b. `2x^2 -x-6`

c. `x^2 -9x-10`

d. `x^2 - 1/4 x`

Giải thích các bước giải:

a. `5x(x^2 -3xy+4y)`

`=5x.x^2-5x.3xy+5x.4y`

`=5x^3-15x^2 y+20xy`

b. `(2x+3)(x-2)`

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

`=2x^2-4x+3x-6)`

`=2x^2 -x-6`

c. `(4x-5)(x+2)-3x(x+4)`

`=4x^2 +8x-5x-10-3x^2 -12x`

`=x^2 -9x-10`

d. `(2x- 1/2 )^2 -(x- 1/3 )(3x- 3/4 )`

`=` `4x^2-2x+1/4-(3x^2-3/4x-x+1/4)`

`=` `4x^2-2x+1/4-(3x^2-7/4x+1/4)`

`=` `4x^2-2x+1/4-3x^2+7/4x-1/4`

`=x^2 - 1/4 x`