Answer
No, it is not true.
Work Step by Step
Given $f(x) = \sqrt x \qquad g(x) = 2 \qquad h(x) = 3$
$f \circ (g + h) = f(2 + 3) = f(5) = \sqrt 5 \approx 2.2361$
$f \circ g + f \circ h = f(2) + f(3) = \sqrt 2 + \sqrt 3 \approx 3.1461$
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