Well there is this function

E(x) = w sqrt[x^2 + 10000] + 50 sqrt[5] - x

Question: Suppose that w = 2 use ure graphics calculator to draw the graph of E(x) and find the x value for which E(x) is a minimum. Specify a suitable domain for x and explain why you have chosen this particular domain.

The domain i BELIEVE to be: 0 < x < 111.8

But i really don't understand the theory as to explaining WHY ..

i need help :(.. pleaseee