<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/baf2a0333c304241929f3be47609082b.png?x-oss-process=image/sharpen,200"/>在<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/3af5e42c36b64ec0b77f12c6f0429852.png?x-oss-process=image/sharpen,200"/>是连续的, 其中<img src="http://jgxm-question.oss-cn-beijing.aliyuncs.com/psst/files/4c287bcd96f741c4b4a1458c9bf3b2cf.png?x-oss-process=image/sharpen,200"/>是符号函数.