∴tanx+tany=-3√3？ ①

tanx tany=4？ ②

∫tan(x+y)=(tanx+tany)/( 1-tanx tany)

=-3√3/( 1-4)

=√3.

∵ From ①tanx+tany=-3√3？

(2) tanx tany = 4

∴ tanx < 0, that is, -π/2 < x < 0.

Chen Shidan < 0, that is, -π/2 < y < 0,

∴-π