7f(f+9)=0

Solution for 7f(f+9)=0 equation:

7f(f+9)=0

We multiply parentheses

7f^2+63f=0

a = 7; b = 63; c = 0;
Δ = b2-4ac
Δ = 632-4·7·0
Δ = 3969
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3969}=63$
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(63)-63}{2*7}=\frac{-126}{14}
=-9
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(63)+63}{2*7}=\frac{0}{14}
=0
$