The sum of the direction cosine of z-axis is ?

Question

anonymous · Answer

could you please elaborate on your question

goformit100 · Answer

Sir this much is the question.

anonymous · Answer

The question is incorrect.

goformit100 · Answer

No sir I have given the question from a book.

anonymous · Answer

do you know what direction cosines are?

goformit100 · Answer

yes...... but unable to solve it :(

anonymous · Answer

well what is it?

dape · Answer

Wouldn't it just be zero? If we do it in cartesian coordinates the dot product of the unit vectors with the z-axis will all be zero, except the z unit vector. The direction cosine is thus the solution to $\cos x=1$, which is zero (if we disregard the "whole turn" solutions). So the sum must also be zero.

dape · Answer

But from the definition of direction cosines it seems pretty trivial.

anonymous · Answer

@dape the direction cosine of z axis would be cos 90
and sum is a function that takes two parameters
the question is invalid

dape · Answer

Yeah, the question is not clear at all.

goformit100 · Answer

Ok... I'll talk to the teacher tomorrow. Thanks Anyways