-72-20a+2a2=0

Solution for -72-20a+2a2=0 equation:

-72-20a+2a^2=0

a = 2; b = -20; c = -72;
Δ = b2-4ac
Δ = -202-4·2·(-72)
Δ = 976
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{976}=\sqrt{16*61}=\sqrt{16}*\sqrt{61}=4\sqrt{61}$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-4\sqrt{61}}{2*2}=\frac{20-4\sqrt{61}}{4}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+4\sqrt{61}}{2*2}=\frac{20+4\sqrt{61}}{4}
$