sin480°.cos150°-sin(-150°).cos(-120°)
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sin780. sin480 + cos120.sin150
=sin(8 x 90+60).sin(5 x90+30) + cos(2 x90 -60).sin(2 x90 +30)
=sin60.cos30 + cos60.(-sin30)
=sin60.cos30 - cos60.sin30
=sin(60 -30)
=sin30
=1/2
=sin(8 x 90+60).sin(5 x90+30) + cos(2 x90 -60).sin(2 x90 +30)
=sin60.cos30 + cos60.(-sin30)
=sin60.cos30 - cos60.sin30
=sin(60 -30)
=sin30
=1/2
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