✔ 最佳答案
1.
sinθ-cosθ=3/4
==>(sinθ-cosθ)^2=(3/4)^2
==>1-2sinθcosθ=9/16
==>2sinθcosθ=7/16
令sinθ+cosθ =k
==>1+2sinθcosθ=k^2
==>k^2=23/16
==>k=(-√23)/4 , (√23/4 不合,因sinθ<0,cosθ<0)
2.
6cos^2θ-sinθ-5=0
==>6(1-sin^2θ)-sinθ-5=0
==>6sin^θ+sinθ-1=0
==>(3sinθ-1)(2sinθ+1)=0
==>sinθ=-1/2 ,(sinθ=1/3不合,因sinθ<0)
==>cosθ=√3/2 (因cosθ>0)
tanθ =(-1/2)/(√3/2)= (-√3)/3
2014-09-21 16:20:19 補充:
2.更正第三行漏字
==>6sin^2θ+sinθ-1=0
2014-09-21 16:25:58 補充:
象限----1-----2-----3-----4
sinθ-------(+)---(+)---(-)----(-)
cosθ-------(+)---(-)---(-)----(+)