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17 January, 18:22

Which of the following equations have complex roots?

A. x^2=-7x-2

B. x^2+3x+9=0

C. x^2=5x-1

D. x^2=-7x+2

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Answers (1)
  1. 17 January, 18:52
    0
    B

    Step-by-step explanation:

    A:

    Completing the square: (x + 7/2) ^2 = - 2 + 49/4 = 41/4, in the next step you'll be square rooting a positive number so it'll have real roots.

    B:

    Completing the square: (x+3/2) ^2 = - 9 + 9/4 = - 27/4, you'll next be square rooting a negative number, so it'll have complex roots

    C:

    Completing the square: (x-5/2) ^2 = - 1 + 25/4 = 21/4, next you'll square root a positive number, so real roots

    D:

    Completing the square: (x+7/2) ^2 = 2 + 49/4 = 57/4, square root a positive number, so real roots.
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