(x+3)(15-5X)=0

Solution for (x+3)(15-5X)=0 equation:

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

We add all the numbers together, and all the variables

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

We multiply parentheses ..

(-5x^2+15x-15x+45)=0

We get rid of parentheses

-5x^2+15x-15x+45=0

We add all the numbers together, and all the variables

-5x^2+45=0

a = -5; b = 0; c = +45;
Δ = b2-4ac
Δ = 02-4·(-5)·45
Δ = 900
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{900}=30$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-30}{2*-5}=\frac{-30}{-10}
=+3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+30}{2*-5}=\frac{30}{-10}
=-3
$