15c-c^2=20

Solution for 15c-c^2=20 equation:

15c-c^2=20

We move all terms to the left:

15c-c^2-(20)=0

We add all the numbers together, and all the variables

-1c^2+15c-20=0

a = -1; b = 15; c = -20;
Δ = b2-4ac
Δ = 152-4·(-1)·(-20)
Δ = 145
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(15)-\sqrt{145}}{2*-1}=\frac{-15-\sqrt{145}}{-2}
$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(15)+\sqrt{145}}{2*-1}=\frac{-15+\sqrt{145}}{-2}
$