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Ask experts Expert Question: pls help me prove sin3A
Reply Forum Index -> Trignometry originally posted here on IIT-JEE / AIEEE community   
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pls help me prove sin3A
    
edison (8935)

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sin 3a = sin (2a + a)

 

=sin 2a cos a + cos 2a sin a


= 2 sin a cos² a + cos 2a sin a

 

= sin a (2 cos² a + cos 2a)


= sin a (2 - 2 sin² a + 1 - 2 sin² a)

 

= sin a (3 - 4 sin² a)


=3 sin a - 4 sin³ a


A paradox is an argument that starts with apparently acceptable assumptions and leads by apparently valid deductions to an apparent contradiction. Since logic admits no contradictions, either the apparently acceptable assumptions are not acceptable, or the apparently valid
deductions are not valid, or the apparent contradiction is not a contradiction. A paradox moves us to reexamine the argument until we find out what is wrong.
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