Solve this quadratic equation by completing the square x^2+6x=18

Question

Solve this quadratic equation by completing the square
x^2+6x=18

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Everleigh 2 weeks 2022-01-08T11:58:36+00:00 2 Answers 0 views 0

Answers ( )

    0
    2022-01-08T11:59:48+00:00

    Answer:

    -8.20 (3sf) , 2.20 (3sf)

    Step-by-step explanation:

    x2 + 6x = 18

    halve the coefficient of x and square it, in this case it is ( 6 / 2 )2 which is 9)

    x2 + 6x + 9 – 9 = 18

    + 9 on both sides,

    ( x + 3 )2 =27

    ok now sq. root both sides

    x + 3 = ± \sqrt{27\\}

    x + 3 = ± 5.196 (4 sf)

    x = -8.20 (3 sf) or x = 2.20 (3sf)

    0
    2022-01-08T11:59:54+00:00

    Answer:

    ( x + 3 )² – 27

    Step-by-step explanation:

    x² + 6x = 18

    → Minus 18 from both sides to get a quadratic equation

    x² + 6x – 18

    ⇒Completed square from is ( x + a )² + b

    ⇒The value of ‘a’ will always be half the ‘b’ value in the equation

    ax² + bx + c

    →( x + 3 )² + b

    Expand out the equation to find ‘b’

    x² + 6x + 9

    We have do something to get from 9 to – 18 which -27

    So the answer is ( x + 3 )² -27

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