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Math Help - Polynomials in Standard Form

  1. #1
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    Polynomials in Standard Form

    Write each function in standard form:
    1. y = (x + 7)(5x + 2)(x - 6)

    I got the answer, but I am not sure if its right. Because I did it two different ways and got two different answers.

    First way, I foiled (x + 7) and (5x + 2), and then foiled (x - 6) and (x - 6). Then I just multiplied the product I got.

    Second way, I foiled (x - 6) and (x - 6), then multiplied the product with (5x + 2) and again, I multiplied the product of that with (x + 7).
    Using the first method, the one I think is right, I got:
    5x^4 - 23x^3 - 250x^2 - 168x + 1836

    Is it right??
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  2. #2
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    (x + 7)(5x + 2)(x - 6)^2
    (x + 7)(5x + 2)(x^2 -12x +36)
    (5x^2 + 37x +14)(x^2 -12x +36)
    (5x^2 + 37x +14)(x^2 -12x +36)
    (5x^4 -23x^3 -250x^2  +1164x +504) I hope
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  3. #3
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    Quote Originally Posted by Power View Post
    Write each function in standard form:
    1. y = (x + 7)(5x + 2)(x - 6)



    Using the first method, the one I think is right, I got:
    5x^4 - 23x^3 - 250x^2 - 168x + 1836

    Is it right??
    Using a long but visible method:
    y = (x + 7)(5x + 2)(x - 6)^2
    y = (x + 7)(5x + 2)(x^2 - 6x - 6x +36)
    y = (x + 7)(5x + 2)(x^2 - 12x + 36)
    y = (x + 7)(5x^3 - 60x^2 + 180x + 2x^2 - 24x + 72)
    y = (x + 7)(5x^3 - 58x^2 + 156x + 72)
    y = (5x^4 - 58x^3 + 156x^2 + 72x + 35x^3 - 406x^2 + 1092x + 504)
    y = 5x^4 - 23x^3 - 250^2 + 1164x + 504?

    Different answer to yours. A third person may be able to confirm but I think mine may be right.

    EDIT: Bobak beat me. He's correct.
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  4. #4
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    Sadly, my arithmetic is very very weak!!!
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