(5a+9)(5a-9)=0

Solution for (5a+9)(5a-9)=0 equation:

(5a+9)(5a-9)=0

We use the square of the difference formula

25a^2-81=0

a = 25; b = 0; c = -81;
Δ = b2-4ac
Δ = 02-4·25·(-81)
Δ = 8100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{8100}=90$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-90}{2*25}=\frac{-90}{50}
=-1+4/5
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+90}{2*25}=\frac{90}{50}
=1+4/5
$