2022高二新课标第三期英语周报答案

21.【必备知识】本题考查的知识是“了解双曲线的定义、几何图形和标淮方程,知道它的简单几何性质(范围、对称性、顶点、离心率、渐近【关键能力】本題考查运算求解能力、逻辑思维能力【解题思路】(1)BF2⊥lIBF1|·|BF2=10,1BF121BF,12=4c2由题一双曲线的定义→|BF|-1BF|=2a两边同时平方→|BF1| IBF212-21BF1·BF21=4a2为2双曲线的离心率为4c2-2×10=4a2b2=5—→双曲线的标准方程(2)直线l与y轴垂直时一→点M与原点O重合—→|MA|=|MB|=2,|AF1|=1,IBF1=52,A =5直线l与y轴不垂直时,设直线l的方程为x=1y-3(t≠0且y515、与双曲线方程联立→(52-4)y2-30y 25=设A(x1,y),B(x2,y2)4>0,y1 y2y1y2=534M(0,÷)x)=A(-3-x1,A u=同理a 得解解:(1)当BF1⊥时,BFP2 1BF12=42,SBA.=1BF1·1BF1=5,可得BF,·IBF2|=10(2分)由双曲线的定义可知,1BF1-1BF21=2a,两边同时平方可得,BF12 |BF212-2BF1·IBF2=4a2,所以4c2-2×10=4a3.①(4分)又双曲线的离心率为2所以。=2②(5分)由①②可得,a2=4,c2=9,所以b2=9-4=5,所以双曲线的标准方程为(6分)(2)当直线l与y轴垂直时,点M与原点O重合,此时1MB2,1Af,1=1,1BF1|=5,所以A=2,n=-3,A 8(7分)当直线l与y轴不垂直时,设直线l的方程为x=ty-3,A(x1,y1)B(x),由题意知/≠0且-21<,将直线l的方程与双曲线方程联立消去x得,(52-4)y2-30xy 25=0,则△90F-4)20 =34=32(8分)易知点M的坐标为(0,),则由赋=A不,可得(x,-3)=X(-3-x,-y),所以A=3-1(9分)同理可得H=l.(10分)所以A =3-1=3.五 y(11分)y1)综上,A 山为定值(12分)

第二节读后续写( One possible version)Fliss immediately took the purse to the local police station with Molly. When they arrivedFliss tied Molly to a fireplug outside and went in herself. She handed the purse to a police officerand explained everything. Greatly touched, he shook her hand and thanked her for doing her duty,promising that he would do his best to find the owner Fliss felt reassured and went back withMolly. The next day, a journalist called to make an appointment for an interview.When the journalist came, they two were on the beach. The journalist was surprised to findthat Molly was picking up litter, following her master. Fliss told the journalist it was on the wayto collecting litter that Molly had found the purse. Hearing this, Molly stopped, wagging her tailas if she understood the whole situation. Having learned about the whole story, the journalist gotto know what they did to protect the local beach. Surprised and impressed, the journalist tooksome pictures. The next day they were on the front page of the newspaper. A minor action couldmake wonders!(162 words)

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