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Math Help - Trig Problems

  1. #1
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    Trig Problems

    Hey guys, Im really stumped on a revision paper I am doing for homework, if you could help me come to the answer I would appreciate it.


    Given that cos x = (3^.5) − 1, find the value of cos 2x in the form a + b(3^.5) ,
    where a and b are integers.

    Given that
    2 cos (y + 30)= 3 sin (y − 30),
    find the value of tan y in the form k 3 where k is a rational constant.
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  2. #2
    Behold, the power of SARDINES!
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    Quote Originally Posted by GregoryT View Post
    Hey guys, Im really stumped on a revision paper I am doing for homework, if you could help me come to the answer I would appreciate it.


    Given that cos x = (3^.5) − 1, find the value of cos 2x in the form a + b(3^.5) ,
    where a and b are integers.

    Given that
    2 cos (y + 30)= 3 sin (y − 30),
    find the value of tan y in the form k 3 where k is a rational constant.
    for the first one use the identity
    \cos(2x)=2\cos^2(x)-1=2(3^{.5}-1)^2-1=....

    for the 2nd use the sum and difference identities for sin and cos

    Good luck.
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  3. #3
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    Given that cos x = (3^.5) − 1, find the value of cos 2x in the form a + b(3^.5) ,
    where a and b are integers.

    hint ... \cos(2x) = 2\cos^2{x} - 1

    Given that
    2 cos (y + 30)= 3 sin (y − 30),
    find the value of tan y in the form k 3 where k is a rational constant.

    hints ...

    \cos(a+b) = \cos{a}\cos{b} - \sin{a}\sin{b}

    \sin(a-b) = \sin{a}\cos{b} - \cos{a}\sin{b}
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  4. #4
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    Guys, I appreciate the help, although is there any chance you can actually work through the question for me and then let me see if I can grasp that. See, I got as far as you are pointing me but Im resitting after being away from maths for a while. = brain freeze.
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