When you dinner, the host will help you clip vegetables, sometimes say that refused to which is difficult. If we have dinner together and adult word, had better let in older people eat first, then before you begin to eat, don't say you don't like this or that kind of food, we Chinese people seldom use knives, forks. We use chopsticks, if you are not used to those please tell the owner, when eating don't want something you like food, also don't chat or laugh, it's impolite.
过圆心做DE的垂线，交DE于点F,
证明△OFD∽△BCA
所以r比AB等于FD比AC
将值代入，后面自己算
We use chopsticks, if you are not used to those please tell the owner, when eating don't want something you like food, also don't chat or laugh, it's impolite.
d
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