Ответ:

N°1.

a)(a+2)(b-3)=ab-3a+2b-6.

б)(х-4)(х+5)=х²+5х-4х-20=х²+х-20.

в)(2х+5)(3х-1)=6х²-2х+15х-5=6х²+13х-5.

N°2.

а)(х+2)(х-5)-3х(1-2х)=х²-5х+2х-10-3х+6х²=7х²-6х-10.

б)(а+3)(а-2)+(а-3)(а+6)=а²-2а+3а-6+а²+6а-3а-18=2а²+4а-24.

в)(х-7)(3х-2)-(5х+1)(2х-4)=3х²-2х-21х+14-(10х²-20х+2х-4)=3х²-2х-21х+14-10х²+18х+4=-7х²-5х+18.

N°3.

a)(2x+6)(7-4x)=(2-x)(8x+1)+15,

14x-8x²+42-24x=16x+2-8x²-x+15,

14x+42-24x=16x+2-x+15,

-10x+42=15x+17, -10x-15x=17-42,

-25x=-25, x=25÷25, x=1.

б)(х+3)(х-2)-(х+4)(х-1)=3х,

х²-2х+3х-6-(х²-х+4х-4)=3х,

х²-2х-6-х²-3х+4=0,

-5х-2=0, -5х=2, х=-2/5=-0,4.