9.(2024四川,文9)设m∈R,过定点A的动直线x+my=0和过定点B的动直线mx-y-m+3=0交于点P(x,y),则|PA|+|PB|的取值范围是( ) A. B. C. D. 答案:B 解析:由题意,得A(0,0),B(1,3), 因为1×m+m×(-1)=0,所以两直线垂直, 所以点P在以AB为直径的圆上,所以PA⊥PB. 所以|PA|2+|...
在取某一头位即出现旋转性眩晕,持续时间一般持续数十秒,改变头位后眩晕可减轻或消失,伴有恶心、呕吐、肢冷汗出等自主神经症状,不伴有耳鸣、耳聋及不稳症状。Dix-hallpike试验,在右侧卧位出现向地性眼震,眼震出现前有数秒钟的潜伏期,眼震持续约30秒,改变头位后眼震消失。最可能考虑的疾病是()
Hello, my name’s Tina. This boy is my11Henry. I’m his sister. We love12and we often go to the school sports club. Doing sports is good for13health. And I14it is also a good way to make friends(交朋友). I like1...