SOLVE FOR U WHERE U IS A REAL NUMBER?

u= squareroot (-2u+15)

4 Answers

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  • 4 years ago
    Best Answer

    u^2 = -2u + 15

    u^2 + 2u - 15 = 0

    u^2 + 5u - 3u - 15 = 0

    u(u + 5) - 3(u + 5) = 0

    (u - 3)(u + 5) = 0

    u - 3 = 0 or u + 5 = 0

    u = 3 or u = -5

    If u = 3 we have:

    3 = sqrt(-2*3 + 15)

    3 = sqrt(-6 + 15)

    3 = sqrt(9)

    TRUE

    If u = -5 we have:

    -5 = sqrt(-2(-5) + 15)

    -5 = sqrt(10 + 15)

    -5 = sqrt(25)

    FALSE, because "sqrt" generally does NOT yield a negative number unless that is specifically stated.

    Final answer: u = 3

  • Caleb
    Lv 6
    3 years ago

    u = -5, 3

  • 4 years ago

    squaring both sides gives, u^2 = -2u+15 so, u^2 + 2u -15 =0 ie (u+5)(u-3)=0

    so u= -5 or u=3

  • 4 years ago

    Seems like u = 3 would satisfy that equation.

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