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Solving Quadratic Equations Using Square Roots  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
Here I have a quadratic equation with no b term so right away I’m thinking I’m going to want to take the square root of both sides of an equation but first I want to get x isolated. I’m going to have to get rid of this 81 piece by adding 81 to both sides, 100x² equals 81.
Next thing I want to do is to get rid of that 100. I’m going to divide both sides by 100 so that I have x² equals 81 over 100. Okay I’m almost there in order to have regular old x and not x² I need to square root both sides. X is going to be equal to the positive and negative square root of 81 over 100.
So depending on what your textbook says you might grab a calculator and do that on your calculator or you might be able to know in your head that the square root of 81 over 100 is 9 over 10. So x is going to be equal to positive and negative 9/10.
The way I would check that is by substituting in one at a time positive 9/10 and then negative 9/10 here and making sure that’s equal to 0.
So guys these problems aren’t too bad if there’s no b term just undo everything that’s been done to x including taking the square root of both sides at the end.
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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.
Sample Problems (14)
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Solving Quadratic Equations Using Square Roots
Problem 1 11,799 viewsSolve:
x² − 225 = 0 
Solving Quadratic Equations Using Square Roots
Problem 2 10,737 viewsSolve:
100x² − 81 = 0 
Solving Quadratic Equations Using Square Roots
Problem 3 8,839 viewsSolve:
x² + 36 = 0 
Solving Quadratic Equations Using Square Roots
Problem 4 1,869 views 
Solving Quadratic Equations Using Square Roots
Problem 5 1,698 views 
Solving Quadratic Equations Using Square Roots
Problem 6 707 views 
Solving Quadratic Equations Using Square Roots
Problem 7 826 views 
Solving Quadratic Equations Using Square Roots
Problem 8 739 views 
Solving Quadratic Equations Using Square Roots
Problem 9 756 views 
Solving Quadratic Equations Using Square Roots
Problem 10 562 views 
Solving Quadratic Equations Using Square Roots
Problem 11 619 views 
Solving Quadratic Equations Using Square Roots
Problem 12 564 views 
Solving Quadratic Equations Using Square Roots
Problem 13 553 views 
Solving Quadratic Equations Using Square Roots
Problem 14 633 views
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