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## Homework Statement

Determine the angle θ between the 300-lb force and the line OC.

I have attached an image of the question

## Homework Equations

P°Q = PQcos(θ)

## The Attempt at a Solution

I tried finding the vectors AB and OA as well as their magnitudes first

O is the origin

A = (9,0,0)

B = (0, 16, 6)

C =(9, 16, 0)

AB = <0-9, 16-0, 6-0>

AB = <-9, 16, 6>

|AB| = sqrt((-9

^{2}) + 162 + 6

^{2})

|AB| = 19.31

OA = <9-0, 0-0, 0-0>

OA = <9, 0, 0>

|OA| = 9

AB°OA = |AB||OA| cos(θ)

<-9, 16, 6>°<9, 0, 0> = (19.31)(9)cos(θ)

arccos(-81/173.79)

θ = 117.78

It says this answer is not correct and I realize that I haven't included the 300-lb force, but how would I take that force into account?