(5-7x)(5+7x) (x+1)(x*2-x+1) (2x-3)(11-6x) (4x+3)(6-x) (9x-25)7

?) `(5-7x)(5+7x)`

`=5(5+7x)-7x(5+7x)`

`=25+35x-35x+49x^2`

`=25+49x^2`

?) `(x+1)(x^2-x+1)`

`=x(x^2-x+1)+1(x^2-x+1)`

$=xx^2-xx+x1+x^2-1x+1.1$

`=x^3-x^2+1x+x^2-1x+1`

`=x^3+(-x^2+x^2)+(1x-1x)+1`

`=x^3+1`

?) `(2x-3)(11-6x)`

`=2x(11-6x)-3(11-6x)`

`=2×11-2x6x-3.11-3.6x`

`=22x-12x^2-33-18x`

`=(22x-18x)-12x^2-33`

`=4x-12x^2-33`

?) `(4x+3)(6-x)(9x-25)7`

`=4x(6-x)+3(6-x).7(9x-25)`

`=24x-4x^2+18-3x.63x-175`

`=24x-4x^2+18-189x^2-175`

`=24x+(-4x^2-189x^2)+(18-175)`

`=24x-193x^2-157`