令x=2sect，dx=2sect*tantdt原积分=∫(2tant)/2sect*2sect*tant dt=2∫tan²tdt=2∫(sec²t-1)dt=2tant-2t+c=√(x²-4)-2arccos(2/x)+c这里x=2sect,cost=2/x,tant=√(x²-4)/2
