-5x(6+2x)=-90

Solution for -5x(6+2x)=-90 equation:

-5x(6+2x)=-90

We move all terms to the left:

-5x(6+2x)-(-90)=0

We add all the numbers together, and all the variables

-5x(2x+6)-(-90)=0

We add all the numbers together, and all the variables

-5x(2x+6)+90=0

We multiply parentheses

-10x^2-30x+90=0

a = -10; b = -30; c = +90;
Δ = b2-4ac
Δ = -302-4·(-10)·90
Δ = 4500
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:

$\sqrt{\Delta}=\sqrt{4500}=\sqrt{900*5}=\sqrt{900}*\sqrt{5}=30\sqrt{5}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-30\sqrt{5}}{2*-10}=\frac{30-30\sqrt{5}}{-20}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+30\sqrt{5}}{2*-10}=\frac{30+30\sqrt{5}}{-20}
$