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Difference of Perfect Squares  Problem 2
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.
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Alissa Fong
M.A. in Secondary Mathematics, Stanford University
B.S., Stanford University
Alissa has a quirky sense of humor and a relatable personality that make it easy for students to pay attention and understand the material. She has all the math tips and tricks students are looking for.
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Sample Problems (8)
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Difference of Perfect Squares
Problem 1 6,833 viewsFactor:
x² − 16 
Difference of Perfect Squares
Problem 2 6,167 viewsFactor:
16x² − 81 
Difference of Perfect Squares
Problem 3 5,261 viewsFactor:
x⁶ − 4y² 
Difference of Perfect Squares
Problem 4 780 views 
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Problem 5 721 views 
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Problem 6 690 views 
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Problem 7 774 views 
Difference of Perfect Squares
Problem 8 801 views
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