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Difference of Perfect Squares - Problem 2 5,347 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

This is a difference of perfect squares problem that’s a little bit different because my leading coefficient isn’t 1, I start out here with 16. But I’m still going to use the same process. I know if I have the difference of perfect squares, it's equal to a plus b times a minus b, plus and minus with my two square roots. So here if I take the square root of 16x² that’s going to be 4x, that will be the fist term in each one of my factors, then I need to take the square root of 81, that’s 9. I’ll have plus 9 and minus 9. That’s it, that’s my final answer.

Again you could write this as 4x minus 9 and plus or you could still switch this and it’s still the same answer because with multiplying it doesn’t matter which one comes first or second.

The key is making sure you take the square root of this first term and the square root of the second term and then writing it with pluses and minuses in between them.