1.由于a^2>10>3 所以椭圆焦点在x轴上,而右焦点F在圆D：(x-2)^2+y^2=1上,所以 F(1,0),c=1,a^2=b^2+c^2=3+1=4 (与a>根号10,有矛盾,警惕!)
椭圆方程为C：X^2/4+y^2/3=1
2.设M(x1,y1),N(x2,y2),向量OM*ON=x1*x2+y1*y2=0
联立两方程X^2/4+y^2/3=1,:x=my+3 得到(3m^2+4)y^2+18my-15=0,两个根分别为y1,y2
y1+y2=-18m/(3m^2+4),y1*y2=-15/(3m^2+4),
x1*x2+y1*y2=(my1+3)(my2+3)+y1*y2=(m^2+1)y1*y2+3m(y1+y2)+9=(m^2+1)*(-15)/(3m^2+4)-3m*18m/(3m^2+4)+9=0,
解得m^2=1/2 于是 m=±根号(1/2).
3.M(x1,y1),N(x2,y2),N1(x2,-y2),P(x0,0),P在直线MM上,则x0=(x1*y2+x2*y1)/(y1+y2)= 2my1*y2+3(y1+y2) =-84m/(3m^2+4)
P到直线l的距离d=|x0-3|/根号(m^2+1),|MN|=根号((x1-x2)^2+(y1-y2)^2)=根号(m^2+1)*根号((y1+y2)^2-4y1*y2)
△PMN的面积S=0.5|MN|*d=0.5*|-84m/(3m^2+4)-3|*根号(-18m/(3m^2+4))^2-4*(-15/(3m^2+4))
.我可以说我不下去了么 .不想算了 .反正思路已经很清晰了.你自己算吧