3(7x+15)(3x-5)=0

Solution for 3(7x+15)(3x-5)=0 equation:

3(7x+15)(3x-5)=0

We multiply parentheses ..

3(+21x^2-35x+45x-75)=0

We multiply parentheses

63x^2-105x+135x-225=0

We add all the numbers together, and all the variables

63x^2+30x-225=0

a = 63; b = 30; c = -225;
Δ = b2-4ac
Δ = 302-4·63·(-225)
Δ = 57600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{57600}=240$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(30)-240}{2*63}=\frac{-270}{126}
=-2+1/7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(30)+240}{2*63}=\frac{210}{126}
=1+2/3
$