How do you find a real part of a complex expression?
Here is an example of what I am looking for
complexExpand[Sqrt[x + I*b]]
(b^2 + x^2)^(1/4) Cos[1/2 Arg[I b + x]] + I (b^2 + x^2)^(1/4) Sin[1/2 Arg[I b + x]],
while there exists expression which does not contain cos or arg (just x and b).