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(1/2)求值,1.sin10sin30sin50sin702.(2cos10-sin20)/cos203.(1+cos20)/2sin20
题目详情
(1/2)求值,1.sin10sin30sin50sin70 2.(2cos10-sin20)/cos20 3.(1+cos20)/2sin20
▼优质解答
答案和解析
(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
=(2cos30cos20+2sin30sin20-sin20]/cos20
=(2*√3/2*cos20+2*1/2sin20-sin20)/cos20
=(√3cos20+sin20-sin20)/cos20
=√3cos20/cos20
=√3
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