# SOLVE FOR U WHERE U IS A REAL NUMBER?

u= squareroot (-2u+15)

### 4 Answers

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- Jeff AaronLv 74 years agoBest 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

- 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

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