Đáp án:
`2)x²y²+4xy-5`
`4)x³-3x²+3x-1`
`5)-x^4+7x³-11x²+6x-5`
Giải thích các bước giải:
`2)(xy-1)(xy+5)`
`=xy(xy+5)-1(xy+5)`
`=x²y²+5xy-xy-5`
`=x²y²+(5xy-xy)-5`
`=x²y²+4xy-5`
`4)(x²-2x+1)(x-1)`
`=x(x²-2x+1)-1(x²-2x+1)`
`=x³-2x²+x-x²+2x-1`
`=x³-(2x²+x²)+(x+2x)-1`
`=x³-3x²+3x-1`
`5)(x³-2x²+x-1)(5-x)`
`=5(x³-2x²+x-1)-x(x³-2x²+x-1)`
`=5x³-10x²+5x-5-x^4+2x³-x²+x`
`=-x^4+(5x³+2x³)-(10x²+x²)+(5x+x)-5`
`=-x^4+7x³-11x²+6x-5`
