a^2-16=15a

Solution for a^2-16=15a equation:

a^2-16=15a

We move all terms to the left:

a^2-16-(15a)=0

a = 1; b = -15; c = -16;
Δ = b2-4ac
Δ = -152-4·1·(-16)
Δ = 289
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{289}=17$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-17}{2*1}=\frac{-2}{2}
=-1
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+17}{2*1}=\frac{32}{2}
=16
$