## Calculus: Early Transcendentals 8th Edition

The functions $f(x) = x+ \sqrt (2-x)$ and $g(u) = u + \sqrt(2-u)$ give exactly the same output values for every input value, so f and g are equal.
These two functions have the same domain, which is from $(-\infty, 2]$. And for the same value input, say x = 2 and u = 2, these two functions give the same result.