y^2-90y-2700=0

Solution for y^2-90y-2700=0 equation:

y^2-90y-2700=0

a = 1; b = -90; c = -2700;
Δ = b2-4ac
Δ = -902-4·1·(-2700)
Δ = 18900
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:

$\sqrt{\Delta}=\sqrt{18900}=\sqrt{900*21}=\sqrt{900}*\sqrt{21}=30\sqrt{21}$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-90)-30\sqrt{21}}{2*1}=\frac{90-30\sqrt{21}}{2}
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-90)+30\sqrt{21}}{2*1}=\frac{90+30\sqrt{21}}{2}
$