题目

阅读理解。 Each nation has many people who help to take care of others. For example, some high school and college students in the U.S.A. often spend many hours as volunteers in the hospitals, orphanages (孤儿院) or rest homes. They read books to the people in these places, or they just visit them and play games with them or listen to their problems. Other young volunteers go and work in the homes of people who are sick or old. They paint, clean up or repair their houses, do their shopping or mow (割,修剪) their lawns. For boys who no longer have fathers, there is an organiz如图,等边三角形OAB的边长为,且其三个顶点均在抛物线E:x2=2py(p>0)上。 (1)求抛物线E的方程;(2)设动直线l与抛物线E相切于点P,与直线y=-1相较于点Q,证明以PQ为直径的圆恒过y轴上某定点。
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