求极限lim(x→0)[tan3x/x]

lim(x→0)[tan3x/x]
=lim(x→0)3[tan3x/3x]
=3
lim(x→1) (x²-2x+1)/(x²-1)
=lim(x→1) (x-1)²/[(x+1)(x-1)]
=lim(x→1) (x-1)/(x+1)
=0