(1)∵a·b=1
∴3cos(θ-π/4)=1
3cosθcosπ/4+3sinθsinπ/4=1
cosθ+sinθ=√2/3①
∵θ∈(π/2,5π/4),
∴cosθ0 θ∈(π/2,π)
①²得到
1+2sinθcosθ=2/9
∴sinθcosθ=-7/9②
①②联立解得
sinθ=(√2+√30)/6
cosθ=(√2-√30)/6
(2)tanθ=sinθ/cosθ=-(8+√15)/7
(1)∵a·b=1
∴3cos(θ-π/4)=1
3cosθcosπ/4+3sinθsinπ/4=1
cosθ+sinθ=√2/3①
∵θ∈(π/2,5π/4),
∴cosθ0 θ∈(π/2,π)
①²得到
1+2sinθcosθ=2/9
∴sinθcosθ=-7/9②
①②联立解得
sinθ=(√2+√30)/6
cosθ=(√2-√30)/6
(2)tanθ=sinθ/cosθ=-(8+√15)/7