how do you solve quadratic equation when b is negative?

Example  

x^2  - 10x  + 25 =  0

x = [ -b ± √[b^2  - 4ac ]  / [2a]

x = [ 10 ± √[(-10)^2  - 4(1)(25)] / [2(1)] =

x = [10  ± √[100 - 100] / 2 =

x = 10 / 2  =  5