(1) y=1/(sinxcosx)=2/sin2x
sin2x≠0
2x≠kπ
则 x≠kπ/2
(2) y=tanx/(1+sinx)
1+sinx≠0 和x≠π/2+kπ
sinx≠-1
x≠3π/2+2kπ
故 x≠π/2+kπ
(2) -cosα
(1) y=1/(sinxcosx)=2/sin2x
sin2x≠0
2x≠kπ
则 x≠kπ/2
(2) y=tanx/(1+sinx)
1+sinx≠0 和x≠π/2+kπ
sinx≠-1
x≠3π/2+2kπ
故 x≠π/2+kπ
(2) -cosα