Why Is the Angle FIE Omitted in the Cylindrical Coordinate Answer?

[bengaltiger14]

Homework Statement

A position vector (between the origin and point (5,2,3) is expressed as r=5(x hat) + 2(y hat) + 3(z hat). Express vector in cylindrical coordinates.

RHO = SQRT(5^2 + 2^2)
FIE = tan-1(y/x)
Z=3

Clearly, RHO = 5.385, FIE = 21.8, and Z=3.

The answer is given is only 5.385(RHO hat) + 3(z hat)

What is the FIE not included in the final answer?

 

[Hao]

In this case, the vector points from the origin. Hence, there is no PHI component, which would be perpendicular to that vector.

 

[bengaltiger14]

Aha! Thank you