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The Discriminant - Concept 12,967 views

Teacher/Instructor Alissa Fong
Alissa Fong

MA, Stanford University
Teaching in the San Francisco Bay Area

Alissa is currently a teacher in the San Francisco Bay Area and Brightstorm users love her clear, concise explanations of tough concepts

The discriminant is the term underneath the square root in the quadratic formula and tells us the number of solutions to a quadratic equation. If the discriminant is positive, we know that we have 2 solutions. If it is negative, there are no solutions and if the discriminant is equal to zero, we have one solution. The discriminant is calculuated by squaring the "b" term and subtracting 4 times the "a" term times the "c" term.

The discriminant is a really handy tool when you think you're getting a weird answer. Here's why. The discriminant tells you how many solutions there are to quadratic equation or how many x intercepts there are for a parabola. It doesn't tell you what those numbers are like what the x intercept values are, it just tells you how many of them there should be. And it sounds like that's not useful but it actually is especially when you're checking your work.
So here is what it looks like. The discriminant is the formula b squared minus 4ac remembering that a, b and c are the coefficients of your quadratic in standard form. It tells you the number of solutions to a quadratic equation. If the discriminant is greater than zero, there are two solutions. If the discriminant is less than zero, there are no solutions and if the discriminant is equal to zero, there is one solution.
This is something you just kind of have to memorize. It goes hand in hand with the quadratic formula. So if you guys have learned that, this will make a lot of sense. If you haven't learnt the quadratic formula yet you'll probably learn it tomorrow in math class. Just know that, what you're looking at is whether or not b squared minus 4ac is greater than zero, less than zero or equal to zero. And it tells me how many answers I should have. It doesn't tell me what the answers are just how many of them I should have in order to get the problem correct.