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Math Help - Help~Trigo Funstion~!!

  1. #1
    Junior Member
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    Post Help~Trigo Funstion~!!

    1.Cos2A+cos4A-cos3A=0, for 0≤A≤360
    2.Show that Cos^-1(A)=Sin^-1 square root (1-A^2), (Inverse Trigonometric Function)
    3.2cos3A-sin3A=Square root 5, for 0≤A≤360
    4.Cos(A-∏/6) + sin (∏/6-A)=1, for 0≤A≤360
    5.Tan3A=cot(∏/3-A), for 0≤A≤360


    Thx for who helpING!!
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  2. #2
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    Please show your work. What have you tried and why do you think it wasn't working?
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  3. #3
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    I stuck at beginning.How to start?
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  4. #4
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    1) Copy down the problem.
    2) Examine a list of known identities for relationships that may prove useful.

    This one can help...

    cos(a+b) = cos(a)cos(b) - sin(a)sin(b)

    3) You dive in and try something. Paralysis never solve problems.
    4) You look for symmetries so you don't have to do the same work twice.

    Hint: With a little effort, you can get the first one to:

    8\cos^{4}(a)-4\cos^{3}(a)-6\cos^{2}(a)+3\cos(a)=0

    If you convert this to look more familiar to the Algebra in you...

    8x^{4}-4x^{3}-6x^{2}+3x=0

    You should be able to solve this by factoring and the Quadratic Formula. (Don't forget your Rational Root Theorem!)
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