+400 The graph of $y = ax^2 + bx + c$ has an axis of symmetry of $x = -1.$ If $a = 2,$ then find $b.$
+1632 The vertex of a parabola lies on the axis of symmetry. Remember that the x-coordinate of the vertex (and the equation of the axis of symmetry) is x = -b/2a.
We know in this problem that -b/2a = x = -1. We also know a = 2, so substituting we get -b/4 = -1, -b = -4, and b = 4.
