-f(3f+7)=0

Solution for -f(3f+7)=0 equation:

-f(3f+7)=0

We multiply parentheses

-3f^2-7f=0

a = -3; b = -7; c = 0;
Δ = b2-4ac
Δ = -72-4·(-3)·0
Δ = 49
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{49}=7$
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-7}{2*-3}=\frac{0}{-6}
=0
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+7}{2*-3}=\frac{14}{-6}
=-2+1/3
$