已知角a∈(π/4,π/2 ),且(4cosa- 3sina )(2cosa- 3sina)=0 (1)tan( a+π/4)(2)co
问题描述:
已知角a∈(π/4,π/2 ),且(4cosa- 3sina )(2cosa- 3sina)=0 (1)tan( a+π/4)(2)co
已知角a∈(π/4,π/2 ),且(4cosa- 3sina )(2cosa- 3sina)=0 (1)tan( a+π/4)(2)cos(π/3-2a)
答
由(4cosa- 3sina )(2cosa- 3sina)=0 得 4cosa- 3sina=0或2cosa- 3sina=0即tana=4/3或2/3 又角a∈(π/4,π/2 ) 则tana∈(1,+∞)故tana=4/3 则cosa=3/5,sina=4/5tan( a+π/4)=(tana+tanπ/4)/(1-tana.tanπ/4 )=...