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\operatorname { sin } 780 ^ { \circ } \operatorname { sin } 480 ^ { \circ } + \operatorname { cos } 240 ^ { \circ } \operatorname { cos } 300 ^ { \circ } = \frac { 1 } { 2 } |
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Answer» 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 |
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