《九章算术》是我国古代内容极为丰富的数学名著。书中有下列问题“今有勾八步，股十五步。问勾中容圆径几何？”其意思为今有直角三角形，勾（短直角边）长为8步，股（长直角边）长为15步，问该直角三角形能容纳的圆形（内切圆）直径是____  步。

    Many children like watching TV．It's very interesting and they can see a lot and know many things about other people．They can also learn from the radio．But they can learn easily with TV．Why? Because they can hear and watch at the same time．But they can't watch anything from the radio(收音机)．TV helps to open children's mind(思想)．They can find better ways to do things．

    Many children watch TV only on Saturday and Sunday nights．They are busy from Monday to Friday．But some children watch TV every night．They go to bed very late．It's not good for their eyes and health.