Consider two straight lines, each of which is tangent to both the circle x2+y2=21 and the parabola y2=4x.
Let these lines intersect at the point Q.
Consider the ellipse whose center is at the origin O(0,0) and whose semi-major axis is OQ.
If the length of the minor axis of this ellipse is 2, then which of the following statement(s) is(are) TRUE?
Answers:A. For the ellipse, the eccentricity is 21 and the length of the latus rectum is 1 · C. The area of the region bounded by the ellipse between the lines x=21 and x=1 is 421(π−2)
Two lines tangent to both x2+y2=21 and y2=4xThey intersect at QEllipse centre O(0,0), semi-major axis =OQMinor axis of the ellipse=2Which statements are true?x2+y2=21:radius 21y2=4x:a=1Tangent to y2=4x:y=mx+m1d(O,line)=∣m∣m2+11=21m2(m2+1)=2⇒m4+m2−2=0(m2+2)(m2−1)=0⇒m2=1m=±1L1:y=x+1,L2:y=−x−1Q=L1∩L2=(−1,0)OQ=(−1)2+02=1semi-major axis a=OQ=1minor axis=2⇒b=22=2112x2+b2y2=1e=1−a2b2=1−21=21Latus rectum=a2b2=12⋅21=1x2+2y2=1⇒y=±211−x2A=∫1/212⋅211−x2dx=2∫1/211−x2dx∫1−x2dx=2x1−x2+sin−1x∫1/211−x2dx=4π−(41+8π)=8π−41A=2(8π−41)=421(π−2)∴Statements (1) and (3) are TRUE