u^2=15u+86

Solution for u^2=15u+86 equation:

u^2=15u+86

We move all terms to the left:

u^2-(15u+86)=0

We get rid of parentheses

u^2-15u-86=0

a = 1; b = -15; c = -86;
Δ = b2-4ac
Δ = -152-4·1·(-86)
Δ = 569
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$u_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-\sqrt{569}}{2*1}=\frac{15-\sqrt{569}}{2}
$
$u_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+\sqrt{569}}{2*1}=\frac{15+\sqrt{569}}{2}
$