This is actually for an engineering class, but it's pretty basic vector addition.
Determine the angle θ between the two cables attached to the post.
I've attached the picture.
The Attempt at a Solution
From the picture:
First, to find F2, I used the angles and the formula cos(α)=(F2x/F2)
To find F1, I used the 35° from the vertical to find the z component, then used the 20° in the xy plane to find the x and y components.
According to the back of the book, the answer is 97.3°. So, I've made a mistake somewhere. Any help finding it would be greatly appreciated.