Câu 2:
`a) -8x(6x+3)+2x(5-3x)`
`=-48x^2-24x+10x-6x^2`
`=-54x^2-14x`
`b) (3x-5)(3x+2)`
`=9x^2+6x-15x-10`
`=9x^2-9x-10`
`c) (10x^2y-8x^2y^3+4x^3y):(-2x^2y)`
`=-5+4y^2-2x`
`d) (2x^3+5x^2-2x+3):(2x^2-x+1)`
`=(2x^3-x^2+x+6x^2-3x+3):(2x^2-x+1)`
`=[x(2x^2-x+1)+3(2x^2-x+1)]:(2x^2-x+1)`
`=(2x^2-x+1)(x+3):(2x^2-x+1)`
`=x+3`
Câu 3:
`a) 5x^3-7x=x(5x^2-7)`
`b) x^2+y^2-49-2xy`
`=(x^2-2xy+y^2)-49`
`=(x-y)^2-7^2`
`=(x-y-7)(x-y+7)`
`c) 8-x^3=(2-x)(4+2x+x^2)`
`d) 3x^2-7x-10`
`=3x^2+3x-10x-10`
`=3x(x+1)-10(x+1)`
`=(x+1)(3x-10)`
Câu 4:
`\qquad 2(x+3)-x^2+3x=0`
`<=> 2(x+3)-x(x+3)=0`
`<=> (x+3)(2-x)=0`
`<=>`\(\left[ \begin{array}{l}x=2\\x=-3\end{array} \right.\)
Vậy `S={2;-3}`
