例4求lm2xsin 3x 解mim2x·sin 3x 令t= 3x 2 sint 2 ==lim 2.. sint = lim 3t 3t3 3t. 31 lim 2 sin x x x  →  求 x x x 31 lim 2 sin →  t t t sin 32 lim0 =  → . 32 = 例 4 解 t x x t 3131 == == 令 t t t sin 31 lim 2 0   →