lim 3x/X-√ x2-3
=lim3x/x-(-x)√(1-3/x^2)) 因为xx趋于负无穷大,所以x提出根号时是正数,所以是-x
=lim3x/x(1+√(1-3/x^2))
=lim3/(1+√(1-3/x^2))
=3/(1+1)
=3/2