当<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/71e426ec0e214cd4baddf957e26b74c2.png?x-oss-process=image/sharpen,200"/>时，下列函数中与<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/1743d4fc276c46189f1ab3ea66be0c92.png?x-oss-process=image/sharpen,200"/>等价的无穷小量是