4r^2-26r=-20

Solution for 4r^2-26r=-20 equation:

4r^2-26r=-20

We move all terms to the left:

4r^2-26r-(-20)=0

We add all the numbers together, and all the variables

4r^2-26r+20=0

a = 4; b = -26; c = +20;
Δ = b2-4ac
Δ = -262-4·4·20
Δ = 356
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{356}=\sqrt{4*89}=\sqrt{4}*\sqrt{89}=2\sqrt{89}$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-26)-2\sqrt{89}}{2*4}=\frac{26-2\sqrt{89}}{8}
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-26)+2\sqrt{89}}{2*4}=\frac{26+2\sqrt{89}}{8}
$