Use the quadratic formula to solve the following equation. (r-3)(r+9)=-9?

(r-3)(r+9)=-9

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  • Rogue
    Lv 7
    6 years ago
    Favorite Answer

    (r − 3)(r + 9)=-9

    => r(r + 9) −3(r + 9)= -9

    => r^2 + 9r −3r − 27 = -9

    => r^2 + 6r − 18 = 0

    now that you have in the form of ax^2 + bx + c = 0 you can use the quadratic formula x = [-b ±√(b^2 − 4ac)]/(2a) in this case a = 1, b = 6, and c = -18

    => x = [-6 ±√(6^2 − 4*1*-18)]/(2*1)

    => x = [-6 ±√(36 +72)]/2

    => x = [-6 ±√(36 * 3)]/2

    => x = [-6 ±6√3]/2

    => x = -3[1 ± √3]

  • Glipp
    Lv 7
    6 years ago

    (r - 3)(r + 9) = -9

    r^2 + 6r - 27 = -9

    r^2 + 6r + 9 = 27

    (r + 3)^2 = 27

    r + 3 = ±3√3

    r = -3 ± 3√3

    r = -3(1 ± √3)

  • Anonymous
    6 years ago

    You have to put it all on one side and then expand. That will make it easier for you to use the formula. Here is a hint: expanded form is r squared + 6r - 18 = 0.

  • Adam
    Lv 5
    6 years ago

    This link has a step by step solution to your problem:

    http://www.symbolab.com/solver/quadratic-equation-...

    Hope this helps

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