Rearranging the above equation, we get:

`cos theta=1/2`

We know the following :

Since

`cos (pi/3) = 1/2`

and `cos θ` is positive in the first and fourth quadrants, we have:

`theta=pi/3`

or

`theta=2pi-pi/3=(5pi)/3`

So `theta=pi/3` or `theta=(5pi)/3`

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