(5x+2)(3x-15)=0

Solution for (5x+2)(3x-15)=0 equation:

(5x+2)(3x-15)=0

We multiply parentheses ..

(+15x^2-75x+6x-30)=0

We get rid of parentheses

15x^2-75x+6x-30=0

We add all the numbers together, and all the variables

15x^2-69x-30=0

a = 15; b = -69; c = -30;
Δ = b2-4ac
Δ = -692-4·15·(-30)
Δ = 6561
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{6561}=81$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-69)-81}{2*15}=\frac{-12}{30}
=-2/5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-69)+81}{2*15}=\frac{150}{30}
=5
$