Đáp án+Giải thích các bước giải:
1)
`(x-4y)(x+4y)+16y^2`
`=x^2-(4y)^2+16y^2`
`=x^2-16y^2+16y^2`
`=x^2`
2)
`(x-y)^2+(x+y)(x-2y)-3y^2`
`=x^2-2xy+y^2+x^2-xy-2y^2-3y^2`
`=(x^2+x^2)-(2xy+xy)+(y^2-2y^2-3y^2)`
`=2x^2-3xy-4y^2`
3)
`(x-1)(x^2-x-1)-x^3+2x^2-1`
`=x^3-2x^2+1-x^3+2x^2-1`
`=(x^3-x^3)+(2x^2-2x^2)+(1-1)`
`=0`
4)
`(x-3)^2+x(x+3)-2x^2+9+4x`
`=x^2-6x+9+x^2+3x-2x^2+9+4x`
`=(x^2+x^2-2x^2)+(3x+4x-6x)+(9+9)`
`=x+18`
5)
`(3x+4)^2-(x-1)(x+1)-8x^2-17`
`=9x^2+24x+16-(x^2-1)-8x^2-17`
`=9x^2+24x+16-x^2+1-8x^2-17`
`=(9x^2-x^2-8x^2)+24x+(16+1-17)`
`=24x`
6)
`(x+5)^2-(x+2)(x+3)-19`
`=(x^2+10x+25)-(x^2+5x+6)-19`
`=x^2+10x+25-x^2-5x-6-19`
`=(x^2-x^2)+(10x-5x)+(25-6-19)`
`=5x`
7)
`(x+y)(x^2-y)-x^3-x^2y+xy`
`=x^3+x^2y-xy-y^2-x^3-x^2y+xy`
`=(x^3-x^3)+(x^2y-x^2y)+(xy-xy)-y^2`
`=-y^2`
8)
`(2x+7)(7-2x)-(x-2)(x+3)+5x^2-55`
`=(-4x^2+49)-(x^2+x-6)+5x^2-55`
`=-4x^2+49-x^2-x+6+5x^2-55`
`=(-4x^2-x^2+5x^2)-x+(49-55+6)`
`=-x`
