某手机电池的电压为3．6V，安时容量为1800mA·h，则该手机电池充满电后所储存的电能为____J．一台电脑接在220V的电路中，通电5h消耗的电能是3．564×105J，则通过它的电流是____mA．

（Ⅰ）求证：AC⊥平面ABB₁A₁；

（Ⅱ）求二面角A﹣C₁D﹣C的平面角的余弦值．

                                                                                Just a Quick Nap 只要打个盹儿
      Do you feel a little sleepy after lunch? Well, that's normal. Your body naturally slows down then. What should you do about it? Don't reach for a coffee! Instead, take a nap.
       It's good to have a daily nap. First of all , you are more efficient（有效的） after napping . You remember things better and make fewer mistakes. Also, you can learn things more easily after taking a nap. A nap may increase your self-confidence（自信） and make you more active . It may even cheer you up. But, there are some simple rules you should follow about taking a nap. First, take a nap in the middle of day, about eight hours after you wake up. Next, a 20-minute nap is best. If you sleep longer, you may fall into a deep sleep. After waking from a deep sleep, you will feel worse. Also, you should set an alarm clock. That way, you can fully relax during your nap. You won't have to keep looking at the clock so you don't oversleep.
       Now，the next time you feel sleepy after lunch , don't get stressed . Put your head down, close your eyes, and catch forty winks.