If the point (2, k) lies outside the circles x2 + y2 + x – 2y – 14 = 0 and x2 + y2 = 13 then k lies in the interval
Given that point (2,k) lies outsides the circles x2 + y2 + x - 2y - 14 = 0 and x2 + y2 = 13.
We know that for a point (a, b) to lie outside the circle S, the condition to be satisfies is S11>0.
Applying S11>0 for 1st circle,
⇒ 22 + k2 + 2 - 2(k) - 14>0
⇒ 4 + k2 - 2k - 12>0
⇒ k2 - 2k - 8>0
⇒ k2 - 4k + 2k - 8>0
⇒ k(k - 4) + 2(k - 4)>0
⇒ (k + 2)(k - 4)>0
We know that the solution set of (x - a)(x - b)>0 for b>a is (- ∞,a)∪(b,∞).
The solution set for k is (- ∞, - 2)∪(4,∞) ..... (1)
Applying S11>0 for 2nd circle,
⇒ 22 + k2 - 13>0
⇒ k2 + 4 - 13>0
⇒ k2 - 9>0
⇒ (k - 3)(k + 3)>0
The solution set for k is (- ∞, - 3)∪(3,∞) ...... (2)
The resultant solution set for k is the intersection of (1) and (2).
⇒ k(((- ∞, - 2)∪(4,∞))∩((- ∞, - 3)∪(3,∞)))
⇒ k((- ∞, - 3)∪(4,∞))
∴The correct option is (c).