(7x+5)(-9x+4)=0

Solution for (7x+5)(-9x+4)=0 equation:

(7x+5)(-9x+4)=0

We multiply parentheses ..

(-63x^2+28x-45x+20)=0

We get rid of parentheses

-63x^2+28x-45x+20=0

We add all the numbers together, and all the variables

-63x^2-17x+20=0

a = -63; b = -17; c = +20;
Δ = b2-4ac
Δ = -172-4·(-63)·20
Δ = 5329
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{5329}=73$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-17)-73}{2*-63}=\frac{-56}{-126}
=4/9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-17)+73}{2*-63}=\frac{90}{-126}
=-5/7
$