10楼: Originally posted by jabile at 2013-12-25 16:42:31
先取a足够大;然后固定a，取b，使得M足够大...

11楼: Originally posted by 我是椰子 at 2013-12-26 18:57:23
当a和b都充分大时，M应该是趋于1吧？...

12楼: Originally posted by jabile at 2013-12-26 20:30:56
不一定啊，比如a=n, b=n^2...

13楼: Originally posted by 我是椰子 at 2013-12-27 10:41:34
关键问题是，题目中的a是0，并不允许其充分大。...

5楼: Originally posted by jabile at 2013-12-25 08:39:18
\int_a^b f^2(x)dx\int_a^b g^2(x)dx\geq ^2
令g(x)=1/f(x),b/a=M,可得，
{1\over b^2} \int_a^b f^2(x)dx
\geq (1-{1\over M})^2{1\over \int_a^b {1\over f^2(x)}dx}
\geq (1-{1\over M})^2 {1\over \int_a ...