令x=3sect,则dx=secttantdt
∫√(x^2-9)dx/x
=∫tantsecttantdt/sect
=∫(tant)^2dt
=∫[(sect)^2-1]dt
=tant-t+C
=3/√(x^2-9)-arccos(3/x)+C
令x=3sect,则dx=secttantdt
∫√(x^2-9)dx/x
=∫tantsecttantdt/sect
=∫(tant)^2dt
=∫[(sect)^2-1]dt
=tant-t+C
=3/√(x^2-9)-arccos(3/x)+C