分式有意义,1-tan²x≠0
tan²x≠1
tanx≠1且tanx≠-1
x≠kπ/2 +π/4 (k∈Z)
函数的定义域为(kπ/2,kπ/2 +π/4)U(kπ/2 +π/4,(k+1)π/2) (k∈Z)