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Solving Quadratic Equations by Factoring  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
All right here’s a problem that I want to solve by factoring. But before I can factor this I need to get this equation that’s equal to 0. I need to subtract 15 from both sides before I can do any factoring. x2 plus 2x take away 15 equals 0. Now I’m looking for two numbers whose product is 15 and whose sum is +2.
So you guys have already practiced factoring a lot you know that the numbers I’m going to want to use are +5 and 3. You know where I did that it’s kind of like Foiling in my head I would have as my outsides 5x, my insides will be 3x added together I get +2x.
Okay now I’m going to use the zero product property and write each one of these terms as equal to 0 and then solve for x to find my solutions. Add 3 to both sides and I would have x equals 3, subtract 5 from both sides and I would have x equals 5.
I think those are my solutions let me just check up top. Make sure that when you substitute in 3, 3² is 9 plus 2, 2 times 3 is 6 it should be equal to 15 good let’s test with 5. 5² is 25, 5 times 2 is 10 and I do indeed get 15 as my answer that told me I did this problem correctly. So solving by factoring what you want to do is make sure that your original problem is set equal to 0 before you do any factoring over here on your trinomial.
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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 (22)
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Solving Quadratic Equations by Factoring
Problem 1 16,019 viewsSolve by factoring:
x² + 4x = 0 
Solving Quadratic Equations by Factoring
Problem 2 13,028 viewsSolve by factoring:
x² + 2x = 15 
Solving Quadratic Equations by Factoring
Problem 3 11,715 viewsSolve by factoring:
x² + 6x + 9 = 0 
Solving Quadratic Equations by Factoring
Problem 4 12,092 viewsSolve by factoring:
3x² − 18x = 27 
Solving Quadratic Equations by Factoring
Problem 5 2,161 views 
Solving Quadratic Equations by Factoring
Problem 6 2,158 views 
Solving Quadratic Equations by Factoring
Problem 7 1,872 views 
Solving Quadratic Equations by Factoring
Problem 8 1,800 views 
Solving Quadratic Equations by Factoring
Problem 9 1,797 views 
Solving Quadratic Equations by Factoring
Problem 10 1,830 views 
Solving Quadratic Equations by Factoring
Problem 11 1,657 views 
Solving Quadratic Equations by Factoring
Problem 12 1,836 views 
Solving Quadratic Equations by Factoring
Problem 13 1,667 views 
Solving Quadratic Equations by Factoring
Problem 14 1,940 views 
Solving Quadratic Equations by Factoring
Problem 15 1,650 views 
Solving Quadratic Equations by Factoring
Problem 16 1,017 views 
Solving Quadratic Equations by Factoring
Problem 17 1,006 views 
Solving Quadratic Equations by Factoring
Problem 18 895 views 
Solving Quadratic Equations by Factoring
Problem 19 1,017 views 
Solving Quadratic Equations by Factoring
Problem 20 940 views 
Solving Quadratic Equations by Factoring
Problem 21 983 views 
Solving Quadratic Equations by Factoring
Problem 22 996 views
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