#1
x=-1/2
y=-3
2*(-1/2)³-1/3*(-3)²=2*(-1/8)-1/3*9=-1/4-3=-3,25
#2
{3a-2b=14
{2a+b=7|*2
+{3a-2b=14
+{4a+2b=14
7a=28|:7
a=4
4*2+b=7
b=7-8
b=-1
#3
(3x+y)(2x-5y)-6(x-y)²=6x²-15xy+2xy-5y²-6(x²-2xy+y²)=
6x²-13xy-5y²-6x²+12xy-6y²=-11y²-xy
(-2x³y)³*(-5x²y)²=-8x^9y³*25x⁴y²=-200x^13y^5
#4
ab+ac-a=a(b+c-1)
4x²-y²+2x-y=(4x²-y²)+(2x-y)=(2x-y)(2x+y)+(2x-y)=(2x-y)(2x+y)
#5
V1-x
V2-y
{2x+y=28
{y=x+4
-{2x+y=28
-{-x+y=4
3x=24|:3
x=8
y=8+4
y=12