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Math Help - [SOLVED] common ratio

  1. #1
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    [SOLVED] common ratio

    ok I thought I got this right but its not working "according to the answer"

    If x - 2 , x + 4 , 5x + 2 are three consecutive terms in a geometric sequence, determine the numerical value(s) of the common ratio(s).
    answer correct answer is -1 and 3

    but if you plug that back in the -1 works but the 3 gives you
    1,7,17?

    I did 5x +2 over x+4 equal to x+4 over x-2
    cross multilpied
    solved for x by factoring and got -1,5 and my ratios are -1 and 5 when I plug them back in.... whats goin on?
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  2. #2
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    Hello, brentwoodbc!

    If x - 2 , x + 4 , 5x + 2 are three consecutive terms in a geometric sequence,
    determine the numerical value(s) of the common ratio(s).
    Correct answer is -1 and 3 . These are values of {\color{blue}r}

    but if you plug that back in the -1 works
    . . but the 3 gives you 1, 7, 17? . You're letting {\color{blue}x = 3}

    I did 5x +2 over x+4 equal to x+4 over x-2
    cross multilpied
    solved for x by factoring and got -1,5 . . . . correct so far!

    and my ratios are -1 and 5 when I plug them back in. . . . . How?
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  3. #3
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    Quote Originally Posted by brentwoodbc View Post
    ok I thought I got this right but its not working "according to the answer"

    If x - 2 , x + 4 , 5x + 2 are three consecutive terms in a geometric sequence, determine the numerical value(s) of the common ratio(s).
    answer correct answer is -1 and 3

    but if you plug that back in the -1 works but the 3 gives you
    1,7,17?

    I did 5x +2 over x+4 equal to x+4 over x-2
    cross multilpied
    solved for x by factoring and got -1,5 and my ratios are -1 and 5 when I plug them back in.... whats goin on?
    If x= -1, then the three numbers are -1-2= -3, -1+ 4= 3, 5(-1)+ 2= -3 so your geometric sequence begins -3, 3, -3. The common ratio is -1.

    If x= 5, then the three numbers are 5-2= 2, 5+ 4= 9, 5(5)+ 2= 27 so your geometric sequence begins 3, 9, 27. The common ratio is 3.
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  4. #4
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    thanks I got my x/common ration mixed up...
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  5. #5
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    thank you
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