椭圆E:x^2/a^2+y^2/b^2=1(a>b>0)与直线x+y-1=0相交于A、B两点,且OA⊥OB(O为坐标原点

3个回答

  • 1、把y=1-x代入x²/a²+y²/b²=1,(a²+b²)x²-2a²x+a²-a²b²=0,x1+x2=2a²/(a²+b²),x1x2=(a²-a²b²)/(a²+b²),把x=1-y代入x²/a²+y²/b²=1,(a²+b²)y²-2b²y+b²-a²b²=0,y1+y2=2b²/(a²+b²),y1y2=(b²-a²b²)/(a²+b²),OA⊥OB,则y1y2/x1x2=-1,(b²-a²b²)/(a²-a²b²)=-1,a²+b²=2a²b²,直线x+y-1=0在x、y轴截距为1,∵a>b>0,且OA⊥OB,∴a>1,0<b<1,椭圆E与圆x²+y²=1的交点,x=±√[(a²-a²b²)/(a²-b²)],y=±√[(a²b²-b²)/(a²-b²)];

    2、(x1-x2)²=4a^4/(a²+b²)²-4(a²-a²b²)/(a²+b²),(y1-y2)²=4b^4/(a²+b²)²-4(b²-a²b²)/(a²+b²),(x1-x2)²+(y1-y2)²=(4a^4+4b^4)/(a²+b²)²-4(a²-a²b²+b²-a²b²)/(a²+b²)=(4a^4+4b^4)/(a²+b²)²=5/2,把b²=a²/(2a²-1)代入解得:a²=2或a²=2/3(舍去),b²=2/3,椭圆E的方程:x²/2+3y²/2=1.