题目

20．在△ABC中，∠A：∠B：∠C=3：4：5，则∠C等于75°． 答案：分析 根据已知条件设∠A=3x，∠B=4x，∠C=5x，然后根据三角形的内角和列方程即可得到结果．解答 解：∵在△ABC中，∠A：∠B：∠C=3：4：5，∴设∠A=3x，∠B=4x，∠C=5x，∵∠A+∠B+∠C=180°，∴3x+4x+5x=180°，∴x=15°，∴∠C=5x=75°，故答案为：75°．点评 本题考查了三角形的内角和，熟练掌握三角形的内角和是“You are welcome to have dinner with me on Sunday,” said John.“But I don’t know where your house is,” said Henry.“It’s easy. You get off the bus. Then cross the road, and take the first turning on the left. Walk for five minutes. Then you will see a big tree. Take the second on the right after the tree. Walk about a hundred metres down this road. There is a big red house. Go past the big house about five hundred metres, and you will see a small yellow house beside a little tree. Open the door with your foot. ”“With my foot?” said Henry, “Why?” “Well, you won’t come to my house empty-handed will you? ” said John.1.“Take the second on the right” means “You .”A. take the second bus on the rightB. must buy something secondlyC. take the second turning on the rightD. go ahead on the right2.How far is it from the big red house to small yellow house? It’s .A. five minutes’ walk B. a hundred minutes’ rideC. about five hundred metresD. about six hundred metres3.Where is John’s house? It is .A. beside a big red houseB. beside a little treeC. on the right after a big treeD. behind a small yellow house4.Why does John ask Henry to open the door with his foot? Because he thinks Henry .A. will carry a lot of things in both handsB. something is wrong with his handsC. have nothing in his handsD. is afraid to open the door with his hands