21解:(1)以F为圆心与相切的圆的方程为(x=)+y2=p21分将y2=2px代入并整理,得4x2+4px-3p2=0即(2x+3p)(2x-p)=0因为x≥0所以x=2代入y2=2px解得y=±P所以点MN的坐标为(小),,-p)所以MN=2p=43分解得p=2故抛物线E的方程为y2=4x…4分(2)设P(n0),直线AB的方程为x=切y+n代入y2=4x并整理得y2-4y-4n=0由题意,得4=16t2+16n>0即t2+n>0设A(,),B(x2,y)则y1+y2=4t,y1y2=-4n·,,…………6分所以AB=√(1+2)(+y)2一4y=√(1+2)(4+)-4(-4m=4+20+25…7分设AB的中点为R(xoy),则y=232=2;xo=tyo+n=2t2+n即R(2t2+n,2t)…………………………8分所以直线RQ的方程为y-2t=-t(x-2t2-n)令y=0,得x=2t2+n+2所以Q(2t2+n+2,0)…9分所以PQ|=|2t2+n+2-n|=2t2+1=2(t2+1)…………………10分由AB=2PQ得41+tn+t=2×2(1+2)解得n=1,适合A=16t2+16n>0即点P的坐标为(1,0)………………12分

第二节: Possible versionA Meaningful DayIt was Sunday and the sun was shining all day. with the intention of caring for the old, my classmates and Idecided to visit the nursing home last weekThe moment we got there we began to clean rooms and washed clothes for the old. after that some of usswept the floor, which made them both happy and excited. Just two hours later, the whole yard was spotlessAs far as I am concerned, this experience is meaningful For one thing, we helped them do something theycouldn t do on their own. For another, tidy and comfortable environment was also created for them, making themfull of delight.It was through this labor that I fully realized that the awareness of respecting the old should be raised

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