k*(k-10)=1

Solution for k*(k-10)=1 equation:

k*(k-10)=1

We move all terms to the left:

k*(k-10)-(1)=0

We multiply parentheses

k^2-10k-1=0

a = 1; b = -10; c = -1;
Δ = b2-4ac
Δ = -102-4·1·(-1)
Δ = 104
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{104}=\sqrt{4*26}=\sqrt{4}*\sqrt{26}=2\sqrt{26}$
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-2\sqrt{26}}{2*1}=\frac{10-2\sqrt{26}}{2}
$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+2\sqrt{26}}{2*1}=\frac{10+2\sqrt{26}}{2}
$