已知:1989x 2 =1991y 2 =1993z 2 ,x>0,y>0,z>0,且 1 x + 1 y + 1 z =1 . 求证: 1989x+1991y+1993z = 1989 + 1991 + 1993 .
拍照语音搜题,微信中搜索"皮皮学"使用
参考答案:
参考解析:
知识点:
皮皮学刷刷变学霸
举一反三
【简答题】Directions: For this part, you are allowed 30 minutes to write an inquiry letter to a friend. You should write at least 150 words following the outline given below. 假设你有一位居住在美国纽约的好友(David Johnson)。你写信...
【简答题】Feeling left out? A reader wrote in to say that she was feeling lonely at break because her best friend wasn’t around.Here’s our advice to her—and to all kids who feel lonely sometimes. It’s hard when...