1. (2x - y)(x + y)=2x²+2xy-xy-y²=2x²+xy-y²
2. (x+5)(x-2)=x²-2x+5x-10=x²+3x-10
3.
a)6(x - 4) - 2=6x-24-2=6x-26
b) 2(x + 1) - 3(x - 1)=2x+2-3x+3=2x-3x+2+3=-x+5
c) -3(y - 2) + 4(y + 2)=-3y+6+4y+8=y+14
d) 5(x - y - 1) - 4(x + 2)=5x-5y-5-4x-8=x-5y-13
e) 2(3a + b) - 2(a - b)=6a+2b-2a+2b=4a+4b
f) 1/2(4x - 4) - 2x=1/2·2(2x-2)-2x=2x-2x-x=-2
g) x(x - 1) - 3(x² - x)=x²-x-3x²+3x=-2x²+2x
h) 5a(a - 3) - 3a(a - 5)=5a²-15a-3a²+15a=2a²