摘要
1.浙江临海市杜桥中学叶明淮来稿（邮编:317016）题:已知x<sup>2</sup>+y<sup>2</sup>≤1,x、y ∈R。求证:3≤|x+y|+|y+1|+|2y-x-4|≤7。证明:如图, 设l<sub>1</sub>:x+y=0,l<sub>2</sub>:y+1=0,l<sub>3</sub>:2y-x-4=0,而点（x,y）满足x<sup>2</sup>+y<sup>2</sup>≤1,可知l<sub>2</sub>≥0,l<sub>3</sub>〈0。当x+y≥0时,u=x+y+y+1-
