若椭圆C1:x^2/a^2 +y^2/b^2=1过点Q(1,1/2)作圆C2:X^2 +Y^2=1的切线,切点分别为A,B,直线AB恰好经若椭圆C1:x^2/a^2 +y^2/b^2=1(a大于b大于0),过点Q(1,1/2)作圆C2:X^2+ Y^2=1有切线,切点分别为A,B,直线AB恰好经过椭
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若椭圆C1:x^2/a^2 +y^2/b^2=1过点Q(1,1/2)作圆C2:X^2 +Y^2=1的切线,切点分别为A,B,直线AB恰好经若椭圆C1:x^2/a^2 +y^2/b^2=1(a大于b大于0),过点Q(1,1/2)作圆C2:X^2+ Y^2=1有切线,切点分别为A,B,直线AB恰好经过椭
若椭圆C1:x^2/a^2 +y^2/b^2=1过点Q(1,1/2)作圆C2:X^2 +Y^2=1的切线,切点分别为A,B,直线AB恰好经
若椭圆C1:x^2/a^2 +y^2/b^2=1(a大于b大于0),过点Q(1,1/2)作圆C2:X^2+ Y^2=1有切线,切点分别为A,B,直线AB恰好经过椭圆的右焦点和上顶点.
求1:椭圆有标准方程;2:若直线l与圆C相切于P,且交椭圆于M、N,求证角MON是纯角.
若椭圆C1:x^2/a^2 +y^2/b^2=1过点Q(1,1/2)作圆C2:X^2 +Y^2=1的切线,切点分别为A,B,直线AB恰好经若椭圆C1:x^2/a^2 +y^2/b^2=1(a大于b大于0),过点Q(1,1/2)作圆C2:X^2+ Y^2=1有切线,切点分别为A,B,直线AB恰好经过椭
1.过点Q(1,1/2)作圆C2:x^2+ y^2=1①的切线,切点分别为A,B,
则AQ^2=1+(1/2)^2-1=1/4,
∴A,B在圆(x-1)^2+(y-1/2)^2=1/4②上,
①-②,2x-1+y-1/4=3/4,
即2x+y-2=0,这是AB的方程,
AB交x轴于点(1,0),交y轴于点(0,2),
直线AB恰好经过椭圆的右焦点和上顶点,
∴c=1,b=2,a^2=5,
∴椭圆方程是x^2/5+y^2/4=1.③
2.设l:xcosu+ysinu=1,y=(1-xcosu)/sinu,④
代入③,4x^2(sinu)^2+5[1-2xcosu+x^2(cosu)^2]=20,
整理得[4+(cosu)^2]x^2-10xcosu-15=0,
设M(x1,y1),N(x2,y2),则x1+x2=10cosu/[4+(cosu)^2],x1x2=-15//[4+(cosu)^2],
由④,y1y2=(1-x1cosu)(1-x2cosu)/(sinu)^2
=[1-(x1+x2)cosu+x1x2(cosu)^2]/(sinu)^2,
1-(x1+x2)cosu+x1x2=[4+(cosu)^2-10(cosu)^2-15]/[4+(cosu)^2]
=-[11+9(cosu)^2]/[4+(cosu)^2]