题目

    A 7-magnitude（震级）earthquake hit Ya'an,Sichuan at 8:02 on April 20, 2013, and it killed at least 196 people and injured more than 11,000.     Together with other students, Yang Xuelan ran out to the playground. She was safe. But all her textbooks and exercise books were buried（埋）in the teaching building. What can we do when an earthquake happens? In fact, there's little we can do to stop natural disasters (自然灾害) such as earthquakes happening. But, some methods can reduce the harm they cause.      ◆ Drop down onto your hands and knees. This way can选修4-4：坐标系与参数方程已知圆在极坐标方程为，直线的参数方程为（为参数）.若直线与圆相交于不同的两点.（Ⅰ）写出圆的直角坐标方程，并求圆心的坐标与半径；（Ⅱ）若弦长，求直线的斜率.