In can be less mental effort if the equation is multiplied by -1 first.
.. x^2 -10x +8 = 0
.. x^2 -10x +25 +8 -25 = 0
.. (x -5)^2 = 17
.. x -5 = ±√17
.. x = 5 ±√17
The values of x that satisfy the given equation are
.. x = 5 -√17 ≈ 0.877
.. x = 5 +√17 ≈ 9.123