(9i+7)(9i-7)=0

Solution for (9i+7)(9i-7)=0 equation:

(9i+7)(9i-7)=0

We use the square of the difference formula

81i^2-49=0

a = 81; b = 0; c = -49;
Δ = b2-4ac
Δ = 02-4·81·(-49)
Δ = 15876
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$i_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$i_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{15876}=126$
$i_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-126}{2*81}=\frac{-126}{162}
=-7/9
$
$i_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+126}{2*81}=\frac{126}{162}
=7/9
$