分子、分母同乘以 √(1+xsinx) + 1。那么上式就等于:
=lim {sin²x * [√(1+xsinx) + 1]}/[(1+xsinx) - 1]
=lim {sin²x * [√(1+xsinx) + 1]}/(xsinx)
=lim {sinx * [√(1+xsinx) + 1]} /x
=lim (sinx /x) * [√(1+xsinx) + 1]
=lim (sinx /x) * lim[√(1+xsinx) + 1]
=1 * lim [√(1+0*0) + 1] 注:当 x → 0 时,lim (sinx /x) = 1
=1 * 2
=2