sin(15゜+θ)=cos(45゜+θ)除tan(45゜+θ),求θ.急用．thank very much!!
回答 (2)
2007-09-04 11:26 pm
參考: My Maths knowledge
2007-09-04 11:38 pm
sin(15゜+θ)=cos(45゜+θ)除tan(45゜+θ)
sin(15+θ)sin(45+θ)=cos^2(45+θ)
(-1/2)(cos(60+2θ)-cos30)=(1/2)(cos(90+2θ)+1)
cos(90+2θ)+cos(60+2θ)=√3/2-1
2cos(75+2θ)cos15=√3/2-1
75+2θ=94 or266
θ=9.5 or95.5 for 0≦θ≦360
sin(15+θ)sin(45+θ)=cos^2(45+θ)
(-1/2)(cos(60+2θ)-cos30)=(1/2)(cos(90+2θ)+1)
cos(90+2θ)+cos(60+2θ)=√3/2-1
2cos(75+2θ)cos15=√3/2-1
75+2θ=94 or266
θ=9.5 or95.5 for 0≦θ≦360
參考: me
收錄日期: 2021-04-14 18:12:29
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https://hk.answers.yahoo.com/question/index?qid=20070904000051KK01402