令x=3sect,则dx=3sect*tant dt于是∫ √(x²-9) /x dx=∫ (3tant*3*tant*sect) /3sect dt=∫ 3tan²tdt=∫ (3tan²t+3-3)dt=∫ 3sec²tdt-3∫ 1dt=3tant-3t+C=√(x²-9...