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Math Help - Function

  1. #1
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    Question Function

    I could really use some help with this function. It's probly really easy but I don't know what I'm doing wrong.

    If f(x)=xsquared+3x, find f(2-a).

    I did it like this.

    f(x)=xsquared+3x
    f(2-a)=(2-a)squared+3(2-a)
    f(2-a)=4-asquared+6-3a
    f(2-a)=-asquared-3a+10

    But my teacher told us that it was.

    -asquared-7a+10

    If you could help me I would really appreciate it. Thanks!
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  2. #2
    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by nick_c View Post
    I could really use some help with this function. It's probly really easy but I don't know what I'm doing wrong.

    If f(x)=xsquared+3x, find f(2-a).

    I did it like this.

    f(x)=xsquared+3x
    f(2-a)=(2-a)squared+3(2-a)
    f(2-a)=4-asquared+6-3a
    f(2-a)=-asquared-3a+10

    But my teacher told us that it was.

    -asquared-7a+10

    If you could help me I would really appreciate it. Thanks!
    Note that \left(2-a\right)^2\neq 2^2-a^2!!!

    It turns out that \left(x-y\right)^2=x^2-2xy+y^2. In your case, x=2 and y=a

    Can you try to take it from here?
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