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![[Post New]](/templates/default/images/icon_minipost_new.gif) 25 Jan 2008 22:23:23 IST
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grouping sin square 12 with sin square 18 and sin square 21 with sin square 9
using the formula
sin(A+B)sin(A-B)=sin square (A)-sin square (B)
we get
1/2[sin12-sin6]
sin square 39 = (1- cos 78)/2
sin square 48 = (1- cos 96)/2
also cos 78= cos (90-12)=sin12
cos96=cos(90+6)= -sin 6
using both adding we get answer =1
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Moderation Team
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