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Thread: Need help with a "completing the square" problem in quadratic factoring!

  1. #1
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    Need help with a "completing the square" problem in quadratic factoring!

    When I try to solve x2+3x-10 just by factoring it from it's standard form I get x=-5 and x=2 which is good. But when I try to check that by using the "completing the square method" when you add (b/2)2 to both sides I get x=5/6 which is completely different as you can see. It is said that the "completing the square method works for any problem.
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  2. #2
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    Re: Need help with a "completing the square" problem in quadratic factoring!

    Add $\displaystyle (b/2)^2$ to both sides of what? So far you don't have an equation. Please show exactly what you did. When I use "complete the square", I get the correct answer.
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  3. #3
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    Re: Need help with a "completing the square" problem in quadratic factoring!

    $\displaystyle x^2+3x-10=0$

    $\displaystyle x^2+3x=10$

    $\displaystyle x^2+3x+\frac{9}{4}=10+\frac{9}{4}$

    $\displaystyle (x+\frac{3}{2})^2=\frac{49}{4}$

    $\displaystyle x+\frac{3}{2}=\frac{7}{2}, \frac{-7}{2}$

    $\displaystyle x=2, -5$
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  4. #4
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    Re: Need help with a "completing the square" problem in quadratic factoring!

    Thanks bean I forgot to square the 4
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