cos43°·cos77°+sin43°·cos167°的值

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cos43°·cos77°+sin43°·cos167°的值

cos43°·cos77°+sin43°·cos167°的值
cos43°·cos77°+sin43°·cos167°的值

cos43°·cos77°+sin43°·cos167°的值
原式=cos43°·cos77°+sin43°·cos(90+77)°=cos43°·cos77°+sin43°·(-sin77°)=cos43°·cos77°-sin43°·sin77°=cos(43+77)°=cos120°= -1/2