设 <img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/b39203180b6e4aad8e8b829056931941.png?x-oss-process=image/sharpen,200"/>是由<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/e545db1a175845a594d6c37d5c89e52b.png?x-oss-process=image/sharpen,200"/>沿<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/14d2db86367a4cfe9f74e5a5dab1d6b0.png?x-oss-process=image/sharpen,200"/>经<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/e212da13a83f456fb58aed6fd3bca2c4.png?x-oss-process=image/sharpen,200"/>到<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/1e4cdf1f0bc74f53bf6022ae4302761a.png?x-oss-process=image/sharpen,200"/>的曲线段，则积分<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/5ac4dd8b7eb6464db630f3e42f9965c7.png?x-oss-process=image/sharpen,200"/>的值为（）.