Let the line L: 2x+y= pass through the point of the intersection P (in the first quadrant) of the circle x2+y2=3 and the parabola x2=2y. Let the line L touch two circles C1 and C2 of equal radius 2 3. If the centres Q1 and Q2 of the circles C1 and C2 lie on the y-axis, then the square of the area of the triangle PQ1Q2 is equal to .
Answer
72
Solution
x2=2y in x2+y2=3: y2+2y-3=0 y=1 (y=-3 rejected) P( 2, 1)
P on L: = 2 2+1=3
Centre (0, k): ∵ L is tangent, distance = radius: |k-3| 3=2 3 k=9 or -3
[figure]
Base Q1Q2=12 (on the y-axis), height = distance of P from the y-axis = 2
Area = 12 12 2=6 2 (Area)2=72
Answer: 72