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Math Help - Quick Question Help

  1. #1
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    Quick Question Help

    I am doing a non-credit assignment and would like to check my answers to see if I have done them correctly, If you can provide help, show steps and/or show me final answer to the following questions it would greatly assist me to see if I am doing these correctly, Thank you!
    Question 1:
    The exact value of cos(105) can be determined using the sum and difference identities. Determine the exact value of cos(105) and express the answer in the form


    Question 2:
    Prove the Following algebraically;





    Question 3:
    Solve the following equation for x, where
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  2. #2
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    Re: Quick Question Help

    For the first one.

    \cos 105 = \cos (60+45)

    Now apply the identity \cos (A+B) = \cos A \cos B - \sin A \sin B
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  3. #3
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    Re: Quick Question Help

    Quote Originally Posted by Prentz View Post
    I would like to check my answers to see if I have done them correctly.
    Then you need to post your working and your answers and we can check them.
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  4. #4
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    Re: Quick Question Help

    Question 3 To get values of x in range 0-360 you need to consider 3x in range 0-1080
    Hence 3x=30,150,390,510,750,870
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  5. #5
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    Re: Quick Question Help

    Write tanx as sinx/cosx, cscx as 1/sinx and cotx as cosx/sinx. Then multiply top and bottom by sinxcosx.
    Should then get sin^2x/cox-cos^2x. Now write sin^2x as 1-cos^2x which factorises to (1-cosx)(1+cosx). Also factorise cosx-cos^2x into cosx(1-cosx). You should see that (1-cosx) cancels out and get the result.
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