2. Three or four quadrants

3 . x≦[(2k+ 1)π]/8

4.(7π/6+2kπ， 1 1π/6+2kπ)

5. Move π/6 to the right

6.①4π

②2π

③π

④π/2

⑤π⑥π/2

9 unfinished

14. 1/5

22.3/5

26.a= (2√3)-4

27.①(0, 1)

②(-∞,- 1)∪(0, 1)

(3) The handwriting is unclear

④(-3,97)

⑤(- 1, 1)∪(2,+∞)

⑥(-2,5)