7d(d-9)=0

Solution for 7d(d-9)=0 equation:

7d(d-9)=0

We multiply parentheses

7d^2-63d=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:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

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