(5x+7)(4x-7)=0

Solution for (5x+7)(4x-7)=0 equation:

(5x+7)(4x-7)=0

We multiply parentheses ..

(+20x^2-35x+28x-49)=0

We get rid of parentheses

20x^2-35x+28x-49=0

We add all the numbers together, and all the variables

20x^2-7x-49=0

a = 20; b = -7; c = -49;
Δ = b2-4ac
Δ = -72-4·20·(-49)
Δ = 3969
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3969}=63$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-63}{2*20}=\frac{-56}{40}
=-1+2/5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+63}{2*20}=\frac{70}{40}
=1+3/4
$