证明cos1/2+cos1/3+.+cos1/n>2/3
问题描述:
证明cos1/2+cos1/3+.+cos1/n>2/3
答
难哦
答
∵cos1/2≈0.8>2/3
∴cos1/2+cos1/3+...+cos1/n>cos1/2>2/3