100=f1+f2

Solution for 100=f1+f2 equation:

100=f1+f2

We move all terms to the left:

100-(f1+f2)=0

We add all the numbers together, and all the variables

-(+f+f^2)+100=0

We get rid of parentheses

-f^2-f+100=0

We add all the numbers together, and all the variables

-1f^2-1f+100=0

a = -1; b = -1; c = +100;
Δ = b2-4ac
Δ = -12-4·(-1)·100
Δ = 401
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{-(-1)-\sqrt{401}}{2*-1}=\frac{1-\sqrt{401}}{-2}
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{401}}{2*-1}=\frac{1+\sqrt{401}}{-2}
$