设该直线的倾斜角为m,则tanm=cosa,即tanm得范围是[-1,1]于是m即为[-π/4,π/4]
首先可得c=p/2.设抛物线方程y^2=2px,由于P点在抛物线上所以P(1/2,根号p)它也在椭圆上于是代入得p/b^2=3/4,b^2=1-c^2,于是2c/(1-c^2)=3/4,c=1/3.c=-3舍去。e=c/a=1/3
Sn=2an+n2-3n-2,,S(n+1)=2a(n+1)+(n+1)^2-3(n+1)-2,后面减去前面得2an=a(n+1)+2n-2。两边同时减去4n得a(n+1)-2(n+1)=2(an-2n)数列an-2n为等比数列,首项为2,2为公比
an-2n=2^n.于是an=2^n+2n.sn=2^1+-----+2^n+2(1+2+。。。。n)=2^(n+1)+n^2+n-2
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