20r^2-60r+25=0

Solution for 20r^2-60r+25=0 equation:

20r^2-60r+25=0

a = 20; b = -60; c = +25;
Δ = b2-4ac
Δ = -602-4·20·25
Δ = 1600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1600}=40$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-60)-40}{2*20}=\frac{20}{40}
=1/2
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-60)+40}{2*20}=\frac{100}{40}
=2+1/2
$