-6(d+3)(d-5)=0

Solution for -6(d+3)(d-5)=0 equation:

-6(d+3)(d-5)=0

We multiply parentheses ..

-6(+d^2-5d+3d-15)=0

We multiply parentheses

-6d^2+30d-18d+90=0

We add all the numbers together, and all the variables

-6d^2+12d+90=0

a = -6; b = 12; c = +90;
Δ = b2-4ac
Δ = 122-4·(-6)·90
Δ = 2304
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2304}=48$
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-48}{2*-6}=\frac{-60}{-12}
=+5
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+48}{2*-6}=\frac{36}{-12}
=-3
$