Đáp án+Giải thích các bước giải:
`a) (x-3)(x+7)-(x+5)(x-1)`
`=x^2+7x-3x-21-x^2+x-5x+5`
`=(x^2-x^2)+(7x-3x+x-5x)-(21-5)`
`=0+0-16`
`=-16`
`b) (x+8)^2-2(x+8)(x-2)+(x-2)^2`
`=(x+8)^2-2.(x+8).(x-2)+(x-2)^2`
`=(x+8-x+2)^2`
`=10^2`
`=100`
`c) x^2(x-4)(x+4)-(x^2+1)(x^2-1)`
`=x^2(x^2-16)-(x^4-1)`
`=x^4-16x^2-x^4+1`
`=-16x^2+1`
`d) (x+1)(x^2-x+1)-(x-1)(x^2+x+1)`
`=x^3+1^3-(x^3-1^3)`
`=x^3+1-x^3+1`
`=2`
