The two structural members, one of which is in tension and the other in compression, exert the indicated forces on joint O. Determine the magnitude R of the resultant R of the two forces and the angle θ which R makes with the positive x axis (measured counterclockwise from the x axis).

I have the resultant force but I don't know how to get theta.


  • $\begingroup$ Do you have the $x$ and $y$ components of the resultant? If so, then just use $\theta=\arctan(y/x)$ $\endgroup$ – Omnomnomnom Sep 4 '13 at 3:23
  • $\begingroup$ My x component is 3.81616. My Y component is -1.07517. When I use arctan(y/x) i get -15.7347. That answer is apparently incorrect. $\endgroup$ – R3alAli Sep 4 '13 at 3:45
  • 1
    $\begingroup$ It could be that they want a positive angle. I'm not sure how many tries you have, but what about $360-15.7347=344.2653$? At any rate, you should definitely get an angle in the lower-right quadrant, so you can't be too far off the right track... $\endgroup$ – Omnomnomnom Sep 4 '13 at 3:49
  • $\begingroup$ You were correct. Thanks for your help. $\endgroup$ – R3alAli Sep 4 '13 at 4:05

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