Show that cos12+cos60+cos84=cos24+cos48 , Mathematics

L.H.S.

=cos 12+cos 60+cos 84

=cos 12+(cos 84+cos 60)

=cos 12+2.cos 72 . cos 12

=(1+2sin 18)cos 12

=(1+2.(√5 -1)/4)cos 12

=(1+.(√5 -1)/2)cos 12

=(√5 +1)/2.cos 12

 
R.H.S

=cos 48+cos 24

=2cos 36. cos 12

=2.(√5 + 1)/4)cos 12

=(√5 +1)/2.cos 12

 L.H.S = R.H.S

Posted Date: 3/9/2013 8:03:08 AM | Location : United States







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