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What positive value of b makes 9^2-bx+4 a perfect square trinomial? How would you solve this problem? Thanks

  • Math -

    9x^2-bx+4

  • Math -

    First of all to be a perfect square, the first and last terms should be perfect squares, and they are!
    so it looks like we had

    (3x ± 2)^2
    for (3x+2)^2 we would get 9x^2 + 12x + 4

    so -bx = 12x
    b = -12

    for (3x - 2)^2 we would get 9x^2 - 12x + 4
    so -bx = -12x
    b = 12

    So b = ± 12

  • Math -

    Thank you!

  • Math -

    Welcome

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