用一根长48厘米的铁丝围成一个最大的正方体框架，这个正方体占地____，在它的表面蒙上铁皮需铁皮____。

已知α∈（﹣π，﹣ $\frac{\pi }{4}$ ），且sinα=﹣ $\frac{1}{3}$ ，则cosα等于（  ）

C

Dear Li Hua,

    How's everything going? Congratulations on your graduation from junior high school!

    I hope you have a great time during the holiday, but you have something important to think about —a plan for your personal growth. Here are some advice for you.

    Firstly, study yourself. Understand what you like, what you value and what you want to be. In studying yourself, you check your strength (长处) and weakness. Find out what you need to prepare for your dream job.

    Secondly, write down your plan. When writing, you can try using Mind Maps (思维导图). It is a good way to help you to think more clearly. And you may find a proper way to work your plan out.

    Thirdly, go over your plan with your teachers, parents or friends. They may give you some advice. Think carefully about their advice and make some changes to your plan if necessary. And then you can go on with it.

    Finally,   ⑵     . For example, if you want to be an English teacher in the future, you should spend more time reading English books, learning more about English culture and practicing your listening and speaking from now on. You can make your dream come true only through hard work.

    You may find it difficult to make the plan now. Don't worry. All you need is just a rough (粗略的) one. Once you enter the senior high school, you'll get a chance to make it better with help of development. So take your time and I believe you will grow into an excellent young man.

    Best wishes!

Yours,

Li Fang