Are these true lines? If so, you can simply find the function of each line and when y1=y2 you have an intersection point. This is also possible with non-linear equations, but it gets more tricky.

EDIT:

To expand on that a bit, if you have two lines defined by the following functions:

Code:

y = 2x + 4
y = x + 1

You may then find the point of intersection by substituting for y and solving for x:

Code:

2x + 4 = x + 1
2x = x - 3
x = -3

So, at x=-3 we know we have a point of intersection. We can prove this by plugging in -3 for x in the two equations and verifying that we get the same result:

Code:

y = 2(-3) + 4
y = -6 + 4
y = -2
y = -3 + 1
y = -2

The two lines intersect at (-3,-2).