Question

1/ Thực hiện phép tính sau :

a) (2x - y)(4x² - 2xy + y²)                                    b) (21x² + 67x - 60) (x - 5)                       

c) (2x² +x - 25)(x² +5x - 2)                                  d) (27x - 8)(6x + 9x² + 4)

Answer 1

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

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

`=8x^3-y^3`

________________________________

`b)(21x^2+67x-60)(x-5)`

`=x(21x^2+67x-60)-5(21x^2+67x-60)`

`=21x^3+67x^2-60x-105x^2-335x+300`

`=21x^3-38x^2-395x+300`

________________________________

`c)(2x^2+x-25)(x^2+5x-2)`

`=2x^2(x^2+5x-2)+x(x^2+5x-2)-25(x^2+5x-2)`

`=2x^4+10x^3-4x^2+x^3+10x^2-2x-25x^2-125x+50`

`=2x^4+11x^3-19x^2-127x+50`

________________________________

`d)(27x-8)(6x+9x^2+4)`

`=27x(6x+9x^2+4)-8(6x+9x^2+4)`

`=16x^2+243x^3+108x-48x-72x^2-32`

`=243x^3-56x^2+60x-32`