The set of values of k for which the circle C:4x2+4y2−12x+8y+k=0 lies inside the fourth quadrant and the point (1,−31) lies on or inside the circle C is :
(A)An empty set
(B)(6,995]
(C)[980,10)
(D)(9,992]✓ Correct
Answer: (D)
Solution
Rewriting the circle equation: x2+y2−3x+2y+4k=0
Center: (23,−1), Radius: r=49+1−4k=213−k
For the circle to exist: k≤13.
Condition 1: Point (1,−31) lies on or inside the circle: 1+91−3−32+4k≤0 4k≤923 k≤992
Condition 2: Circle lies in fourth quadrant means center is in fourth quadrant and circle doesn't touch axes. The center (23,−1) is in the fourth quadrant. For the circle to not touch the x-axis: r<1, so 213−k<1, giving k>9.
Combining all conditions: k∈(9,992]
Answer: (D)
JEE Main · 2022 · 27 Jun 2022 · Shift 2 · Single correct option