9f^2-90=25f

Solution for 9f^2-90=25f equation:

9f^2-90=25f

We move all terms to the left:

9f^2-90-(25f)=0

a = 9; b = -25; c = -90;
Δ = b2-4ac
Δ = -252-4·9·(-90)
Δ = 3865
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-25)-\sqrt{3865}}{2*9}=\frac{25-\sqrt{3865}}{18}
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-25)+\sqrt{3865}}{2*9}=\frac{25+\sqrt{3865}}{18}
$