ACT Trick for Quadratics: How to Quickly Find the yIntercept of a Parabola
To save time when graphing a quadratic function on the ACT Math test, you can quickly find the location of the yintersept of the parabola based on the sign of the variable c.
The variable c is the constant term of the quadratic equation, y = ax^{2} + bx + c.
Keep the following rules in mind:

When c is positive, the yintercept is positive. In other words, the parabola intersects the yaxis above the origin.

When c is negative, the yintercept is negative. That is, the parabola intersects the yaxis below the origin.
Warning: Be clear that in a quadratic function, c is the yintercept. In contrast, in a linear function
b is the yintercept.
Example
Which of the following could be a graph of the function y = –x^{2} + 5x – 2?
(A)
(B)
(C)
(D)
(E)
In this equation, c = –2, so the yintercept is below the yaxis. As a result, you can rule out Choices (C), (D), and (E). Additionally, a = –1, so the parabola is concave down. So you also can rule out Choice (A), which makes the correct answer Choice (B).