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Thread: Factorise

  1. #1
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    Smile Factorise

    -3(5x - 8)^2 + 27
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  2. #2
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    $\displaystyle -3(5x - 8)^2 + 27$
    Foil it first
    $\displaystyle -3[25x^2-80x+64]+27 $
    Distribute the -3
    $\displaystyle -75x^2+240x-192+27 $
    $\displaystyle -75x^2+240x-165 $
    Factor out a -15
    $\displaystyle -15[5x^2-16x+11] $
    factor
    $\displaystyle -15(x-1)(5x-11) $
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  3. #3
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    Quote Originally Posted by Joker37 View Post
    -3(5x - 8)^2 + 27
    Easier to take out -3 as a common factor and then DOTS.

    $\displaystyle -3(5x - 8)^2 + 27 = -3[(5x - 8)^2 - 9]$

    $\displaystyle = -3[(5x - 8)^2 - 3^2]$

    $\displaystyle = -3[(5x - 8 + 3)(5x - 8 - 3)]$

    $\displaystyle = -3(5x - 5)(5x - 11)$

    $\displaystyle = -15(x-1)(5x-11)$.
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