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Math Help - symbols as variables

  1. #1
    klg
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    symbols as variables

    The question is:

    For all positive integers x, let x▲ be defined to be (x-1)(x+1). Which of the following is equal to 6▲-5▲?
    A) 2▲ +1▲
    B) 3▲+2▲
    C) 4▲+3▲
    D) 5▲+4▲
    E) 6▲+5▲

    I was under the impression that if I substituted (x-1)(x+1) for ▲ and worked the problem, I could come up with the answer, but I must be missing something. I am aware that the minus sign in the original problem is the subtraction of a binomial, but that did not help.
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  2. #2
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    Re: symbols as variables

    Quote Originally Posted by klg View Post
    The question is:

    For all positive integers x, let x▲ be defined to be (x-1)(x+1). Which of the following is equal to 6▲-5▲?
    A) 2▲ +1▲
    B) 3▲+2▲
    C) 4▲+3▲
    D) 5▲+4▲
    E) 6▲+5▲
    The easy way to answer this is to note that (x-1)(x+1)=x^2-1.
    So 6\blacktriangle=36-1=35.
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  3. #3
    klg
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    Re: symbols as variables

    Thank you, for some reason I thought it was more difficult.
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