Now whatever the exact shape of the graph's curve,made by joining these points,it must have a high point.Point"X"is the very maximum anyone can learn in the day.And this represents the optimum,the best,amount of work to do. It is the best possible compromise betweenadequate time at the books and fatigue.Fatigue is an absolutely real thing;one can't escape it or ignore it.If you try to ignore it and press yourself to work past the optimum,you will only get on this downward slope and achieve less than the best--and then become very tired and lose your power of concentration.

1翻译:It is the best possible compromise betweenadequate time at the books and fatigue.
2我想知道怎样才能猜出fatigue的意思.

between 和 adequate 之间应该有空格。

直接翻译一定会很别扭，这句话的意思是：“这是一个最佳的折衷方案，既能让你花足够的时间在书本上，又不至于太过疲劳（而影响学习效率）”。文章的愿意大概是，对很多学生而言，"adequate time at the books" 和 "fatigue" 是有矛盾的，如果时间花够了，你的体力会透支；如果要保证体力，时间又不够用，所以你要尽量折衷一下。

fatigue 我觉得不是很好猜，但是猜出它是一个负面的词，还是有可能的，因为文章里提到 escape it，你不会想逃离一个好的东西。文中还提到，如果你忽略之，你会achieve less，显然是个坏的结果。总之，还是记住它吧，也是一个常用字。