4x-2y=8 ---> -2y=8-4x multiply it by -1 so that the negative 2 would be positive then it would be like this --> 2y=-8+4x then divide it by 2. magiging y=-4+2x.
sa -10x+5y=-20 nman, multiply it by -1 para maging 10x-5y=20.
10x-5(-4+2x)=20
10x+20-10x=20
10x-10x=20-20
0=0
