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Math Help - SAT math page 684 #16

  1. #1
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    SAT math page 684 #16

    Let *x* (very wierd if you ask me) be defined as *x* = x^2-x for all values of x. If *a*=*a-2*, what is the value of a?

    a)1
    b)1/2
    c)3/2
    d)6/5
    e)3

    I got this: (a-2)^2-(a-2) = a^2-3a+6. But the answer I got for a isn't in the choices. Any tips? Thanks in advance
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    I'm not sure what this problem is asking. Is it asking where does "x" and "a" intersect or what is x(a)? Is "*" a symbol in the book that is suppose to represent some type of operation like those problems with squares and triangles that you are suppose to figure out?

    Lastly, from your wording of this problem it doesn't look like "x" is related with "a" in any shape or form.
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    Quote Originally Posted by Linnus View Post
    I'm not sure what this problem is asking. Is it asking where does "x" and "a" intersect or what is x(a)? Is "*" a symbol in the book that is suppose to represent some type of operation like those problems with squares and triangles that you are suppose to figure out?

    Lastly, from your wording of this problem it doesn't look like "x" is related with "a" in any shape or form.
    "*" IS a symbol in the book that is suppose to represent some type of operation like those problems with squares and triangles that you are suppose to figure out

    Yeah i know, I don't think x and a are related at all. This is why I'm confused by this question.
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  4. #4
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    Oh if * is an operation then

    if *x*= x^2-x
    and
    *a*= *a-2*
    then
    a^2-a=(a-2)^2-(a-2)

    Solve for a.
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  5. #5
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    Quote Originally Posted by fabxx View Post
    Let *x* (very wierd if you ask me) be defined as *x* = x^2-x for all values of x. If *a*=*a-2*, what is the value of a?

    a)1
    b)1/2
    c)3/2
    d)6/5
    e)3

    I got this: (a-2)^2-(a-2) = a^2-3a+6. But the answer I got for a isn't in the choices. Any tips? Thanks in advance
    You only have to use the given definition twice:

    *a* = a - a and

    *a-2* = (a-2) - (a-2)

    That means you have to solve the equation:

    a - a = (a-2) - (a-2)

    I've got a = 3
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