Giải thích các bước giải:
`a, \ 2x^2-5x-2x(x+1)`
`=2x^2-5x-2x^2-2x`
`=(2x^2-2x^2)-(5x+2x)`
`=-7x`
`b, \ (3x-2)^2-(3x-1)^2`
`=(3x-2-3x+1)(3x-2+3x-1)`
`=-1.(6x-3)=-6x+3`
`c, \ x(5-x)+5x(x-1)`
`=5x-x^2+5x^2-5x`
`=(5x^2-x^2)+(5x-5x)`
`=4x^2`
`d, \ (x+3y)(x-3y)-9y(x-y)`
`=x^2-9y^2-9xy+9y^2`
`=x^2+(9y^2-9y^2)-9xy`
`=x^2-9xy`
`e, \ (x+1)^2-(x+2)(x-2)`
`=x^2+2x+1-x^2+4`
`=(x^2-x^2)+2x+1+4`
`=2x+5`
`f, \ (x+2)^2-(x+3)(x-2)+10`
`=x^2+4x+4-(x^2-2x+3x-6)+10`
`=x^2+4x+4-x^2-x+6+10`
`=(x^2-x^2)+(4x-x)+4+6+10`
`=3x+20`
