摘要： 1.设$x,y,z$是三个复数,定义\[d(x, y)=\frac{|x-y|}{\sqrt{\left(1+|x|^{2}\right)\left(1+|y|^{2}\right)}}.\]求证:\[d(x, y) \leq d(x, z)+d(z, y).\] 2.设$a_{1}, a_{2}, 阅读全文