(99-y)y=5

Solution for (99-y)y=5 equation:

(99-y)y=5

We move all terms to the left:

(99-y)y-(5)=0

We add all the numbers together, and all the variables

(-1y+99)y-5=0

We multiply parentheses

-1y^2+99y-5=0

a = -1; b = 99; c = -5;
Δ = b2-4ac
Δ = 992-4·(-1)·(-5)
Δ = 9781
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(99)-\sqrt{9781}}{2*-1}=\frac{-99-\sqrt{9781}}{-2}
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(99)+\sqrt{9781}}{2*-1}=\frac{-99+\sqrt{9781}}{-2}
$