15n=-5n^2

Solution for 15n=-5n^2 equation:

15n=-5n^2

We move all terms to the left:

15n-(-5n^2)=0

We get rid of parentheses

5n^2+15n=0

a = 5; b = 15; c = 0;
Δ = b2-4ac
Δ = 152-4·5·0
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$n_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-15}{2*5}=\frac{-30}{10}
=-3
$
$n_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+15}{2*5}=\frac{0}{10}
=0
$