title: 一道数学题计算:arctan1/3+arctan1/2=____ 
desc: 计算:arctan1/3+arctan1/2=_________.
answer: 答案:π/4
  
  解:设x=arctan(1/3),y=arctan(1/2),则
  tanx=1/3,tany=1/2,0<x<π/2,0<y<π/2.
  因此0<x+y<π,且
  tan(x+y)=(tanx+tany)/(1-tanxtany)
  =(1/3+1/2)/(1-1/3×1/2)
  =1
  因此
  x+y=π/4
  即原式=π/4。