To solve this, we will set the equations equal to eachother. We know that since the two expressions, and both equal , then the expressions are equal. (Somebody comment what property that is, I forgot what it's called) So:
The point where 2 lines intersect contain (x,y) coordinates that are equal for both equations. By setting the 2 equations equal to each other, it is same as equating the 2 y-values, which we know they are equal at point of intersection.
