-4(a^2-13a+20)=0

Solution for -4(a^2-13a+20)=0 equation:

-4(a^2-13a+20)=0

We multiply parentheses

-4a^2+52a-80=0

a = -4; b = 52; c = -80;
Δ = b2-4ac
Δ = 522-4·(-4)·(-80)
Δ = 1424
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:

$\sqrt{\Delta}=\sqrt{1424}=\sqrt{16*89}=\sqrt{16}*\sqrt{89}=4\sqrt{89}$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(52)-4\sqrt{89}}{2*-4}=\frac{-52-4\sqrt{89}}{-8}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(52)+4\sqrt{89}}{2*-4}=\frac{-52+4\sqrt{89}}{-8}
$