7f(9f-5)=0

Solution for 7f(9f-5)=0 equation:

7f(9f-5)=0

We multiply parentheses

63f^2-35f=0

a = 63; b = -35; c = 0;
Δ = b2-4ac
Δ = -352-4·63·0
Δ = 1225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1225}=35$
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-35)-35}{2*63}=\frac{0}{126}
=0
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-35)+35}{2*63}=\frac{70}{126}
=5/9
$