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    postergirl's Avatar
    postergirl Posts: 1, Reputation: 1
    New Member
    		  
    #1

    Feb 28, 2008, 03:20 PM
    trig functions
    how would I justify these identity::confused: (show all the work... )

    sin4x=8cos^3xsinx-4


    also...

    tanx(1-sin^2x)-1/2sin2x


    thanks!!
    galactus's Avatar
    galactus Posts: 2,271, Reputation: 282
    Ultra Member
    		  
    #2

    Feb 28, 2008, 06:10 PM
    I can give you a good start on #1. Use the addition formula for sine.

    Then use . Then use

    Then you're all set.:)
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