Đáp án_Giải thích các bước giải:
`7)` `(x-3)(x+3)-(x-3)^2`
`=x^2-3^2-(x^2-2*x*3+3^2)`
`= x^2-9-x^2+6x-9`
`=(x^2-x^2)+6x-(9+9)`
`=6x-18`
`=6(x-3)`
`8)` `(x-1)^2(x+2)-(x-2)(x^2+2x+4)`
`=(x^2-2x+1)(x+2)-(x-2)(x^2+2x+2^2)`
`=x^2*x+x^2*2-2x*x-2x*2+1*x+1*2-(x^3-2^3)`
`=x^3+2x^2-2x^2-4x+x+2-x^3+2^3`
`=(x^3-x^3)+(2x^2-2x^2)+(x-4x)+(2+8)`
`=-3x+10`
`9)` `4x(x-3)-3x(2+x)`
`=4x*x-4x*3-(3x*2+3x*x)`
`=4x^2-12x-6x-3x^2`
`=(4x^2-3x^2)-(12x+6x)`
`=x^2-18x`
`=x(x-18)`
`10)` `2x(5x+2)+(2x-3)(3x-1)`
`=2x*5x+2x*2+2x*3x-2x*1-3*3x-3*(-1)`
`=10x^2+4x+6x^2-2x+9x+3`
`=(10x^2+6x^2)+(4x-2x-9x)+3`
`=16x^2-7x+3`
`11)` `(x-1)^2-(x+2)(x-2)`
`=x^2-2*x*1+1^2-(x^2-2^2)`
`=x^2-2x+1-x^2+4`
`=(x^2-x^2)-2x+(4+1)`
`=-2x+5`
`12)` `5y(2y-1)-(3y+2)(3-3y)`
`=5y*2y-5y*1-(3y*3-3y*3y+2*3-2*3y)`
`=10y^2-5y-9y+9y^2-6+6y`
`=(10y^2+9y^2)+(6y-5y-9y)-6`
`=19y^2-8y-6`
`13)` `(2x+3)^2-2(2x+3)(x-2)+(x-2)^2`
`=(2x)^2+2*2x*3+3^2-(2*2x*x-2*2x*2+2*3*x-2*3*2)+x^2-2*x*2+2^2`
`=4x^2+12x+9-4x^2+8x-6x+12+x^2-4x+2^2`
`=(4x^2-4x^2+x^2)+(12x+8x-6x-4x)+(9+12+4)`
`=x^2+10x+25`
`=x^2+2*x*5+5^2`
`=(x+5)^2`
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