-3y(y+5)=15

Solution for -3y(y+5)=15 equation:

-3y(y+5)=15

We move all terms to the left:

-3y(y+5)-(15)=0

We multiply parentheses

-3y^2-15y-15=0

a = -3; b = -15; c = -15;
Δ = b2-4ac
Δ = -152-4·(-3)·(-15)
Δ = 45
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{45}=\sqrt{9*5}=\sqrt{9}*\sqrt{5}=3\sqrt{5}$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-3\sqrt{5}}{2*-3}=\frac{15-3\sqrt{5}}{-6}
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+3\sqrt{5}}{2*-3}=\frac{15+3\sqrt{5}}{-6}
$