1) 5x(2x-3)-(6-x)(7-2x)=10х²-15х-(42-12х-7х+2х²)=
=10х²-15х-42+12х+7х-2х²=8х²+4х-42
2) 2a(a-2)-(3a-1)(2-4a)=2а²-4-(6а-12а²-2+4а)=
=2а²-4-6а+12а²+2-4а=14а²-10а-2
3) 4x(x-3)-(x-4)(x+3)=4х²-12х-(х²+3х-4х-12)=
=4х²-12х-х²-3х+4х+12=3х²-11х+12
