I've met this difficult question while answering some problems related to vector analysis. The question goes like this:
"Find in rectangular components the unit vector which is in the direction of $\bar E$ at $P(1,2,-2)$ if $\bar E = x^2 + y^2 + z^2$.
$$\frac{x}{\sqrt{y^2 + z^2}}a_x + \frac{y}{\sqrt{x^2 + z^2}}a_y + \frac{z}{\sqrt{x^2 + y^2}}a_x"$$
I have no idea where to start, so how do you answer this question?