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  • Algebra homework (year 9)
  • thegreatape
    Free Member

    t^2 – (t-9)^2 = 9

    everyone
    Free Member

    t^2 – t^2 + 18t – 81 = 9
    18t=90
    t=5

    thegreatape
    Free Member

    Smashing, thanks. Where does the 18t come from?

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    thegreatape
    Free Member

    Don’t worry, I’ve got it, wasn’t squaring the brackets properly. Hannah says thanks!

    Murray
    Full Member

    (A+B)^2=A^2+B^2+2AB

    thegreatape
    Free Member

    Ok last bit, why is it +18t not -18t ?

    thegreatape
    Free Member

    The first minus cancels the one within the brackets?

    chambord
    Free Member

    When you multiply out the brackets you get

    t^2 – (t^2 – 18t + 81) = 9

    So negate everything in the brackets

    t^2 – t^2 + 18t – 81 = 9

    thegreatape
    Free Member

    Ok, got it now. Cheers

    Murray
    Full Member

    (A-B)^2=(A-B)(A-B)=a^2-ab-ba+b^2=a^2+b^2-2ab

    smatkins1
    Free Member

    A few more steps shown in the working out might help….

    t^2 – (t – 9)^2 = 9

    t^2 – (t – 9)(t – 9) = 9

    t^2 – (t^2 – 18t + 81) = 9

    t^2 – t^2 + 18t – 81 = 9

    18t – 81 = 9

    18t = 90

    t = 5

    A common mistake would be to not take the step in line 4.

    thegreatape
    Free Member

    That was my second mistake (forgetting 2AB being my first).

    Many thanks, we’re onto English now!

Viewing 12 posts - 1 through 12 (of 12 total)

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