36=25+c^2-2*5*c*0.5

Solution for 36=25+c^2-2*5*c*0.5 equation:

36=25+c^2-2*5c*0.5

We move all terms to the left:

36-(25+c^2-2*5c*0.5)=0

We get rid of parentheses

-c^2+2*5c*0.5-25+36=0

We add all the numbers together, and all the variables

-1c^2+2*5c*0.5+11=0

Wy multiply elements

-1c^2+5c+11=0

a = -1; b = 5; c = +11;
Δ = b2-4ac
Δ = 52-4·(-1)·11
Δ = 69
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{-(5)-\sqrt{69}}{2*-1}=\frac{-5-\sqrt{69}}{-2}
$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(5)+\sqrt{69}}{2*-1}=\frac{-5+\sqrt{69}}{-2}
$