0=-16f^2+6400

Solution for 0=-16f^2+6400 equation:

0=-16f^2+6400

We move all terms to the left:

0-(-16f^2+6400)=0

We add all the numbers together, and all the variables

-(-16f^2+6400)=0

We get rid of parentheses

16f^2-6400=0

a = 16; b = 0; c = -6400;
Δ = b2-4ac
Δ = 02-4·16·(-6400)
Δ = 409600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{409600}=640$
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-640}{2*16}=\frac{-640}{32}
=-20
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+640}{2*16}=\frac{640}{32}
=20
$