-7j(j-9)=0

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

-7j(j-9)=0

We multiply parentheses

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

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