Find the direction of the resulatnt vector

[Arshad_Physic]

Hello everyone, here is a question of which Part b is giving me a headache + tension! :) My teacher only gave us 2 days to do so much homework - one day left! :) Its impossible to take help from him...

Homework Statement

Consider four vectors ~F1, ~F2, ~F3, and ~F4,
where their magnitudes are
F1 = 50 N,
F2 = 29 N,
F3 = 27 N, and
F4 = 58 N.

Let
theta1 = 150 degrees,
theta2 = -140 degrees,
theta3 = 24 degrees, and
theta4 = -66 degrees, measured from the positive x axis
with the counter-clockwise angular direction
as positive.

What is the magnitude of the resultant vec-
tor ~F , where ~F = ~F1 + ~F2 + ~F3 + ~F4? Answer
in units of N.

I found the answer to his part:

-17.259 i and -35.645 j , with a magnitude of 39.604

My online homework accepted this answer :)

...BUT...


(part 2 of 2)
What is the direction of this resultant vector
~F?

Note: Give the angle in degrees, use coun-
terclockwise as the positive angular direction,
between the limits of -180 degrees and +180 degrees from
the positive x axis. Answer in units of degrees.

Homework Equations

I tried doing: tan θ = -35.645/-17.259 - θ=64.164 °

The Attempt at a Solution

I tried doing: tan θ = -35.645/-17.259 - θ=64.164 ° - The answer proved out to be wrong...And thus I can now score a maximum of 93% on this question! :(

I have NO IDEA as to how to solve it - I looked in google, but to no avail...All help would be appreciated! :)

Thanks

Arshad

 

[rl.bhat]

Resultant is in the third quadrant. So theta should be -180 + 64 degrees.

 

[Arshad_Physic]

You are right! THANKS for the help! :)