phase shift & circuits

1. The problem statement, all variables and given/known data

An RLC circuit has a resistance of 2.0 kΩ, a capacitance of 8.0 µF, and an inductance of 9.0 H. If the frequency of the alternating current is 4.0/π kHz, what is the phase shift between the current and the voltage?
A) -1.6 rad
B) -1.5 rad
C) 36 rad
D) 3.1 rad

2. Relevant equations

Tan-1 (XL-Xc/R)

3. The attempt at a solution

at first i thought that since current phasors lag by 90 degrees that it may be -1.5 rads. but that isn’t correct.
then i used the the inverse tangent equation above in hopes of finding the angle which came out to be 88.4 degrees (which is about 1.5 rads)
i then took the 88.4 degrees and subtracted it from 90 degrees, because I thought it might turn out a correct answer because the phasors are perpendicular to each other. but that gives you 1.6 which is not correct either.
I’m not sure what equation to use …

http://ift.tt/1pu10Lo

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