a2-15a=-15

Solution for a2-15a=-15 equation:

a2-15a=-15

We move all terms to the left:

a2-15a-(-15)=0

We add all the numbers together, and all the variables

a^2-15a+15=0

a = 1; b = -15; c = +15;
Δ = b2-4ac
Δ = -152-4·1·15
Δ = 165
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-\sqrt{165}}{2*1}=\frac{15-\sqrt{165}}{2}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+\sqrt{165}}{2*1}=\frac{15+\sqrt{165}}{2}
$