Vertex Formula: The graph of y = ar2 + bx + c has the line a = - as its axis of symmetry. The x-coordinate of the vertex is . = -20 _ b. You can find the y by plugging a into your equation. Example 2: Find the vertex and the axis of symmetry for the following functions. a) y = 2x2 + 4x b) y =-x2+4x -5