Online Test Banks
Score higher
See Online Test Banks
Learning anything is easy
Browse Online Courses
Mobile Apps
Learning on the go
Explore Mobile Apps
Dummies Store
Shop for books and more
Start Shopping

ACT Trick for Quadratics: How to Quickly Find the y-Intercept of a Parabola

To save time when graphing a quadratic function on the ACT Math test, you can quickly find the location of the y-intersept of the parabola based on the sign of the variable c.

The variable c is the constant term of the quadratic equation, y = ax2 + bx + c.

Keep the following rules in mind:

  • When c is positive, the y-intercept is positive. In other words, the parabola intersects the y-axis above the origin.

  • When c is negative, the y-intercept is negative. That is, the parabola intersects the y-axis below the origin.

Warning: Be clear that in a quadratic function, c is the y-intercept. In contrast, in a linear function


b is the y-intercept.


Which of the following could be a graph of the function y = –x2 + 5x – 2?











In this equation, c = –2, so the y-intercept is below the y-axis. 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).

  • Add a Comment
  • Print
  • Share
blog comments powered by Disqus

Inside Sweepstakes

Win $500. Easy.