(1/2)求值,1.sin10sin30sin50sin70 2.(2cos10-sin20)/cos20 3.(1+cos20)/2sin20
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(1/2)求值,1.sin10sin30sin50sin70 2.(2cos10-sin20)/cos20 3.(1+cos20)/2sin20
(1/2)求值,1.sin10sin30sin50sin70 2.(2cos10-sin20)/cos20 3.(1+cos20)/2sin20
(1/2)求值,1.sin10sin30sin50sin70 2.(2cos10-sin20)/cos20 3.(1+cos20)/2sin20
(2cos10-sin20)/cos20=[2cos(30-20)-sin20]/cos20
=(2cos30cos20+2sin30sin20-sin20]/cos20
=(2*√3/2*cos20+2*1/2sin20-sin20)/cos20
=(√3cos20+sin20-sin20)/cos20
=√3cos20/cos20
=√3
默,你写的太不清楚了
sin10sin30sin50sin70
=cos10sin10sin30sin50sin70/cos10
=(1/2)sin20sin30sin50cos20/cos10
=(1/4)sin40sin30cos40/cos10
=(1/8)sin80sin30/cos10
=(1/8)cos10sin30/cos10
=(1/8)sin30
=1/16
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