-5x(x-6)=15

Solution for -5x(x-6)=15 equation:

-5x(x-6)=15

We move all terms to the left:

-5x(x-6)-(15)=0

We multiply parentheses

-5x^2+30x-15=0

a = -5; b = 30; c = -15;
Δ = b2-4ac
Δ = 302-4·(-5)·(-15)
Δ = 600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{600}=\sqrt{100*6}=\sqrt{100}*\sqrt{6}=10\sqrt{6}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(30)-10\sqrt{6}}{2*-5}=\frac{-30-10\sqrt{6}}{-10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(30)+10\sqrt{6}}{2*-5}=\frac{-30+10\sqrt{6}}{-10}
$