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    Need some help for this trig.

    2 \sin \ x \sin \ 5x = \cos \ 4x

    Thanks.
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    (Original post by uer23)
    Need some help for this trig.

    2 \sin \ x \sin \ 5x = \cos \ 4x

    Thanks.
    The second equality should help.

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    (Original post by steve2005)
    The second equality should help.

    The second ones got a minus in front. :confused:
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    (Original post by uer23)
    The second ones got a minus in front. :confused:
    Multiply by minus one.
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    The only formula that I can see (which might work that is) is 2sinAsinB = -[cos(A+B)] - cos(A-B)

    Will give it a go and see what comes out.
 
 
 
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Updated: January 15, 2010
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