I do believe you need the EXACT values.

First, this is an 8-15-17 PYTHAG TRIPLE. Therefore, based on the fact that theta is in Quadrant IV, and that:  we get: 

Now, I can't determine if you want:    

Answer by ikleyn(52803)   (Show Source): You can put this solution on YOUR website!
 .

Use the given information to determine the values of sin(2*theta)​, cos(2*theta), and tan(2*theta).

cos theta=8/17; The terminal side of theta lies in quadrant IV.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~







        The solution in the post by @MowMow has two deficiencies.





        First, it is FATALLY incorrect.





        Second, in his post, the educational part of the solution disappeared in full.



        So, I came to provide a correct solution to this problem in the form as it should be 



        (as it is expected to be).





 

Since   = 8/17  and angle  is in quadrant IV,

     =  =  =  = 

                     =  =  = .


Notice that we us sign  '-'  at the square root since angle  is in quadrant IV, 
where 'sin' is negative.


Now   =  =  =  = -0.8304.

     (compare this correct approximate value with incorrect value of 0.8304 in the post by @MowMow).



For  ,  use the formula

      =  =  = 

                       =  =  =  =   = -0.5571.



For ,  use

      =  =  =  = 1.4907.

     (compare this correct approximate value with incorrect value of -1.4907 in the post by @MowMow).




Solved, and you have clear instructions/guidance on how to do the solution.







/////////////////////////////////////////////////////







@MowMow, it is clear from your post, that you 





        - don't know right-angled triangles



        - don't know Pythagorean triangles



        - do not understand the meaning of this assignment



        - and do'n't know (have no idea) on how to solve it correctly.





I observed your contribution to the forum,





and with 179% confidence I can say that you have no necessary knowledge to be a Math tutor.





I ask you STOP posting to this forum.







 

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