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22 August, 20:31

What's x (x-9) = 10?

a) x = 20, x = - 2

b) x = 65, x = - 56

c) x = - 10, x = 1

d) x = 10, x = - 1

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Answers (2)
  1. 22 August, 21:01
    0
    Hi Laysia

    x (x - 9) = 10

    x² - 9x = 10

    x² - 9x - 10 = 0

    Factor left side

    (x + 1) (x-10)

    Now we can set the factors equal to 0

    x + 1 = 0 or x - 10 = 0

    x = 0 - 1 or x = 0 + 10

    x = - 1 or x = 10

    Answer : x - 1 or x = 10

    The correct option is : D

    Let me know if you have any further questions.
  2. 23 August, 00:11
    0
    Expand and put them all on one side in decreasing order of degree of x:

    x^2 - 9x - 10 = 0

    -9 = 1 - 10

    -10 = 1 * (-10)

    so (x+1) (x-10) = 0

    So

    x+1=0

    (x = - 1)

    And

    x-10=0

    (x=10)

    So the solutions are 10 and - 1 which is d.
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