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Math Help - factoring

  1. #1
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    factoring

    Does this solve to a real number?


    10x^2+9x-9=0
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  2. #2
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    Why factor? The quadratic formula will answer that for you. You don't even need to use the entire formula!
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  3. #3
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    Yeah, the quadratic formula will work and is simpler to explain. As far as factoring goes, here is what to do.

    10x^2+9x-9=0

    First you want to find what two numbers who's sum is 9 and when multiplied equal -90. Those two numbers are -6 and 15.

    Then the problem works out as such...

    (10x^2-6x) + (15x-9)

    2x(5x-3) + 3(5x-3)

    Therefore, it should factor out to (2x+3)(5x-3)=0. Your answers should be x = -(3/2) or (3/5).
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  4. #4
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    Quote Originally Posted by galanm View Post
    Does this solve to a real number?


    10x^2+9x-9=0
    The only restriction to be a single or a pair of real numbers; if you write a general equation a\cdot{x^2}+b\cdot{x}+c=0 and \sqrt{b^2-4\cdot{ac}}\geq{0} then your solution is a pair of different real numbers if is strictly large than zero or a single real number if it's equal to zero
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  5. #5
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    Quote Originally Posted by some_nerdy_guy View Post
    Yeah, the quadratic formula will work and is simpler to explain. As far as factoring goes, here is what to do.

    10x^2+9x-9=0

    First you want to find what two numbers who's sum is 9 and when multiplied equal -90.
    No, they must multiply to -9, not -90.

    Those two numbers are -6 and 15.

    Then the problem works out as such...

    (10x^2-6x) + (15x-9)

    2x(5x-3) + 3(5x-3)

    Therefore, it should factor out to (2x+3)(5x-3)=0. Your answers should be x = -(3/2) or (3/5).
    You've solved the wrong problem!
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  6. #6
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    Huh? It's not wrong, I plugged in the answers and they checked out.

    10x^2+9x-9=0

    ax^2+b+c=0

    You multiply 'a' and 'c' which would be 10 and -9 and will equal -90. Then you see what two numbers when added together will have a sum of 'b' and when multiplied together will equate 'ac' (in this case, -90). How are you concluding that they should equal -9?
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