15=3y(y+2)

Solution for 15=3y(y+2) equation:

15=3y(y+2)

We move all terms to the left:

15-(3y(y+2))=0


We calculate terms in parentheses: -(3y(y+2)), so:

3y(y+2)

We multiply parentheses

3y^2+6y

Back to the equation:

-(3y^2+6y)


We get rid of parentheses

-3y^2-6y+15=0

a = -3; b = -6; c = +15;
Δ = b2-4ac
Δ = -62-4·(-3)·15
Δ = 216
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:

$\sqrt{\Delta}=\sqrt{216}=\sqrt{36*6}=\sqrt{36}*\sqrt{6}=6\sqrt{6}$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-6)-6\sqrt{6}}{2*-3}=\frac{6-6\sqrt{6}}{-6}
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-6)+6\sqrt{6}}{2*-3}=\frac{6+6\sqrt{6}}{-6}
$