Question

sin(-1071')sin99'+sin(-171')sin(-261')-cot1089'cot(-630')等于？ 括号里（'）代表度

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Answer 1

sin(-1071)sin99+sin(-171)sin(-261)
=sin(-1071+3*360)sin(90+9)+sin(-180+9)sin(-360+99)
=sin9cos9-sin(180-9)sin(90+9)
=1-sin9cos9
=1-1
=0