5=10x-x^2

Solution for 5=10x-x^2 equation:

5=10x-x^2

We move all terms to the left:

5-(10x-x^2)=0

We get rid of parentheses

x^2-10x+5=0

a = 1; b = -10; c = +5;
Δ = b2-4ac
Δ = -102-4·1·5
Δ = 80
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{80}=\sqrt{16*5}=\sqrt{16}*\sqrt{5}=4\sqrt{5}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-4\sqrt{5}}{2*1}=\frac{10-4\sqrt{5}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+4\sqrt{5}}{2*1}=\frac{10+4\sqrt{5}}{2}
$