y^2-26y+81=0

Solution for y^2-26y+81=0 equation:

y^2-26y+81=0

a = 1; b = -26; c = +81;
Δ = b2-4ac
Δ = -262-4·1·81
Δ = 352
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{352}=\sqrt{16*22}=\sqrt{16}*\sqrt{22}=4\sqrt{22}$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-26)-4\sqrt{22}}{2*1}=\frac{26-4\sqrt{22}}{2}
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-26)+4\sqrt{22}}{2*1}=\frac{26+4\sqrt{22}}{2}
$