(7x-15)(3x+20)=0

Solution for (7x-15)(3x+20)=0 equation:

(7x-15)(3x+20)=0

We multiply parentheses ..

(+21x^2+140x-45x-300)=0

We get rid of parentheses

21x^2+140x-45x-300=0

We add all the numbers together, and all the variables

21x^2+95x-300=0

a = 21; b = 95; c = -300;
Δ = b2-4ac
Δ = 952-4·21·(-300)
Δ = 34225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{34225}=185$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(95)-185}{2*21}=\frac{-280}{42}
=-6+2/3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(95)+185}{2*21}=\frac{90}{42}
=2+1/7
$