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The Quadratic Formula - Problem 3 4,954 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

Okay I’m going to try to solve this equation using the quadratic formula. So the first thing I’m going to do is find x equals -b which is going to become +2, plus or minus square root of my b² so I’ll have 4 take away 4 times my a term, take away my c term all divided by 2 times 1. That’s the set up. From here on it's just simplifying.

X is equals to 2 plus or minus the square root of 4 take away 8. You guys look, 4 take away 8 is -4. I have a square root of a negative number. That is not a real solution. So I’m done with this problem. I don’t have to do any more math. I just write on my paper no real solutions because this parabola if I were to graph it, this parabola would never cross the x axis.

I could confirm this by looking at the discriminant. So maybe you guys have already learnt the discriminant is b squared minus 4ac and since I had a negative discriminant that would tell me I have no real solutions. If you have no idea what I’m talking about with this discriminant business don’t worry you could skip ahead and watch that video or you could just trust me that when you have the square root of a negative number that just means you have no real solutions. You’re done.

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