(2COS20-SIN10)/SIN80等于多少
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(2cos20-sin80)/sin80
=[2cos20-sin(90-10)]/sin(90-10)
=(cos20+cos20-cos80)/cos10
=[cos20-(cos80-cos20)]/cos10
={cos20-[-2sin (80+20)/2 sin (80-20)/2]}/cos10
=(cos20+2sin50sin30)/cos10
=(cos20+sin50)/cos10
=[cos20+sin(90-40)]/cos10
=(cos20+cos40)/cos10
=[2cos (40+20)/2 cos (40-20)/2]/cos10
=(2cos30cos10)/cos10
=√3
=[2cos20-sin(90-10)]/sin(90-10)
=(cos20+cos20-cos80)/cos10
=[cos20-(cos80-cos20)]/cos10
={cos20-[-2sin (80+20)/2 sin (80-20)/2]}/cos10
=(cos20+2sin50sin30)/cos10
=(cos20+sin50)/cos10
=[cos20+sin(90-40)]/cos10
=(cos20+cos40)/cos10
=[2cos (40+20)/2 cos (40-20)/2]/cos10
=(2cos30cos10)/cos10
=√3
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