To find points of intersection, we need to use simultaneous equations.
y = 2x   --- 1
y = [tex] x^{2} [/tex] - 3   --- 2
Sub 1 into 2,
2x = [tex] x^{2} [/tex] - 3
0 = [tex] x^{2} [/tex] - 2x - 3
[tex] x^{2} [/tex] - 2x - 3 = 0
Factorise,
(x - 3)(x + 1) = 0
Let each bracket equal to 0,
x - 3 = 0               x + 1 = 0
     x = 3                     x = -1
Sub 3 into equation 1,
y = 2(3)
   = 6
Now sub -1 into equation 1,
y = 2(-1)
   = -2
Therefore, your two y values are -2 and 6
Hope this helped! Ask me if there's any part of the working you don't understand :)