# Homework Help: Angle between vectors help

1. Sep 26, 2007

### rafael_josem

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

The figure shows a mast and parts of the equipments of a sailboat. The elements CD and EF belongs to the same plane, CD has 7.5m of lenght and has an angle of 45º with a vertical line that passes by C. When $$\theta$$ = 15º the tension in the rope AB is 230N.

http://img128.imageshack.us/img128/8149/problemas3.th.jpg [Broken]

a) find the angle between the ropes AB and BD

2. Relevant equations

ABcos($$\theta$$) = A.B

Where bold letters represent vectors.

3. The attempt at a solution

I started by finding the coordinates of points A, B and D.

A = (0.5,0,-3)
B = (x, 22, 0)
D = ?

I get lost finding the x coordinate for B and the coordinate of D. With these coordinates I can find the vectors that I need to apply the equation above by doing the following:

AB = (x - 0.5)i + (22-0)j + (0 + 3)k

Any ideas?

Thanks

Last edited by a moderator: May 3, 2017