10x+3y=12 and 10x=-12-3y

10x+3y=12 and 10x=-12-3y

~Put equations directly underneath each other.

10x+3y=12

10x=-12-3y

~Move - 3y to the other side of the equation so that both x and y are on the same side < - 2nd equation.

10x+3y=-12

10x+3y=12

~subtract equations from one another.

0 = - 24

Due to the fact that when you try to add / subtract these equations together and you get zero, there are infinite solutions.

:-)