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Math Help - solving trigo without calculator

  1. #1
    Member helloying's Avatar
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    solving trigo without calculator

    Evaluate without the use of calculator, \sin [ \cos^{-1} (1/2) + \sin^{-1} (4/5) ]
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by helloying View Post
    Evaluate without the use of calculator, \sin [ \cos^{-1} (1/2) + \sin^{-1} (4/5) ]
    \cos(\pi/3)=1/2 (that's cos of 60 degrees, you are supposed to know this)

    If \theta=\arcsin(4/5) then \sin(\theta)=4/5 and \cos(\theta)=3/5 (think 3-4-5 triangle)

    So new you want to know:

    \sin [ \pi/3 + \theta ]

    and you should be able to find this using the usual trig identity for the sine of a sum.

    CB
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