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-   -   Trigonometric equations (https://www.askmehelpdesk.com/showthread.php?t=379542)

  • Jul 24, 2009, 11:28 PM
    liang11
    trigonometric equations
    Prove (Sin5A - Sin4A)/(Cos4A + Cos5A) = Tan A/2
  • Jul 25, 2009, 01:33 AM
    Unknown008

    Convert all the '5A' and '4A' into simple angles, then half angles.





  • Jul 25, 2009, 09:23 PM
    liang11
    Quote:
    Originally Posted by unknown008 View Post
    convert all the '5a' and '4a' into simple angles, then half angles.





    i still don't understand... do u have the solutions?
  • Jul 26, 2009, 12:43 AM
    tej pratap sing
    Quote:
    Originally Posted by liang11 View Post
    i still don't understand...do u have the solutions?
    cos(A+B)=cosAcosB-sinAsinB
  • Jul 26, 2009, 11:53 AM
    tej pratap sing

    sinC-sinD=2cosC+D/2 . SinC-D/2
    cosC+cosD=2cosC+D/2 . CosC-D/2
    apply this formula in question i.e
    sin5A-sin4A 2cos9A/2 .sinA/2 sinA/2
    -------------- = --------------------- = --------- = tanA/2
    cos4A+cos5A 2cos9A/2 . CosA/2 cosA/2

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