9r(r-7)=0

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

9r(r-7)=0

We multiply parentheses

9r^2-63r=0

a = 9; b = -63; c = 0;
Δ = b2-4ac
Δ = -632-4·9·0
Δ = 3969
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3969}=63$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-63)-63}{2*9}=\frac{0}{18}
=0
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-63)+63}{2*9}=\frac{126}{18}
=7
$