math

9^x - 4 X 3^x = 45. Find x

In words:

9 raised to the power x minus 4 multiplied by 3 raised to the power x is equal to 45. Find x.

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  1. or
    (3^x)^2 - 4(3x) -45 = 0
    let 3^x = y

    y2 - 4y - 45 = 0
    (y-9)(y+5) = 0
    y = 9 or y = -5

    3^x = 9
    x = 2
    or
    3^x = -5, which has no solution.

    so x = 2

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