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

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

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

We multiply parentheses ..

(+21x^2-35x+15x-25)=0

We get rid of parentheses

21x^2-35x+15x-25=0

We add all the numbers together, and all the variables

21x^2-20x-25=0

a = 21; b = -20; c = -25;
Δ = b2-4ac
Δ = -202-4·21·(-25)
Δ = 2500
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2500}=50$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-50}{2*21}=\frac{-30}{42}
=-5/7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+50}{2*21}=\frac{70}{42}
=1+2/3
$