If the equation is in vertex form:
1) If the vertex is on the x-axis, there is one root (a double root)
2) If the vertex is above the x-axis and the parabola rises, there are no real roots.
3) If the vertex is above the x-axis and the parabola falls, there are two real roots.
4) If the vertex is below the x-axis and the parabola rises, there are two real roots.
5) If the vertex is below the x-axis and the parabola falls, there are no real roots.