y^2+15y=100

Solution for y^2+15y=100 equation:

y^2+15y=100

We move all terms to the left:

y^2+15y-(100)=0

a = 1; b = 15; c = -100;
Δ = b2-4ac
Δ = 152-4·1·(-100)
Δ = 625
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{625}=25$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-25}{2*1}=\frac{-40}{2}
=-20
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+25}{2*1}=\frac{10}{2}
=5
$