a,(5x ²-4x) (x-2) d,(x ²-2xy+y ²) (x-y) g,(1-3x ²+x) (x ²-5+x)
b,(3x-5) (2x+11)-(2x+3) (3x+7) e,(x ²+2xy+y ²) (x+y) h,(x-5x ²) (x ²+6x+4)
c,(25x²+10y+4y²) (5x-2y) f,6x²-(2x+5) (3x-2) i,(4x²-7x+2) (x²+2x-1)
Đáp án + Giải thích các bước giải:
`a)` `(5x^2-4x)(x-2)`
`=5x^3-10x^2-4x^2+8x`
`=5x^3-14x^2+8x`
`b)` `(3x-5)(2x+11)-(2x+3)(3x+7)`
`=6x^2+33x-10x-55-(6x^2+14x+9x+21)`
`=6x^2+33x-10x-55-6x^2-14x-9x-21`
`=-76`
`c)` `(25x^2+10y+4y^2)(5x-2y)`
`= [(5x)^2+5x*2y+(2y)^2](5x-2y)`
`=(5x)^3-(2y)^3=125x^3-8y^3`
`d)` `(x^2-2xy+y^2)(x-y) = (x-y)^2(x-y)`
`=(x-y)^3=x^3-3x^2y+3xy^2-y^3`
`e)` `(x^2+2xy+y^2)(x+y)=(x+y)^2(x+y)=(x+y)^3`
`=x^3+3x^2y+3xy^2+y^3`
`f)` `6x^2-(2x+5)(3x-2)`
`=6x^2-(6x^2-4x+15x-10)`
`=6x^2-6x^2+4x-15x+10`
`= -11x+10`
`g)` `(1-3x^2+x)(x^2-5+x)`
`=x^2-5+x-3x^4+15x^2-3x^3+x^3-5x+x^2`
`=17x^2-5-4x-3x^4-2x^3`
`h)` `(x-5x^2)(x^2+6x+4)`
`=x^3+6x^2+4x-5x^4-30x^3-20x^2`
`=-5x^4-29x^3-14x^2+4x`
`i)` `(4x^2-7x+2)(x^2+2x-1)`
`=4x^4+8x^3-4x^2-7x^3-14x^2+7x+2x^2+4x-2`
`=4x^4+x^3-16x^2+11x-2`