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`
