Check my calculations ^_^

I keep trying this question over and over again, and keep getting the wrong answer. I was wondering if somebody would be nice enough to check my calculations, and see where I went wrong (or if I’m going about it the wrong way!)

Find the minimum distance from the parabola y=x^2 to the point (5,0).

D = √[(x2-x1)^2 + (y2-y1)^2]

I substituted in points (5,0) and (x, x^2)

D = √[(x-5)^2 + x^2

D = √2x^2 - 10x + 25

d/dx = (4x-10)/ [blahblah not important]

0 = 4x-10

4x=10

x=10/4

Substituting this into the D formula doesn't give the right answer ... the answr is apparently 4.06

Thanks! :)