JEE Challenger
More from Conic Sections

Statements on Lines as Chords and Diameters of Circle

Consider
L1:2x+3y+p−3=0L_1 : 2x + 3y + p - 3 = 0
L2:2x+3y+p+3=0L_2 : 2x + 3y + p + 3 = 0
where pp is a real number, and C:x2+y2+6x−10y+30=0C : x^2 + y^2 + 6x - 10y + 30 = 0.

STATEMENT-1 : If line L1L_1 is a chord of circle CC, then line L2L_2 is not always a diameter of circle CC.

and

STATEMENT-2 : If line L1L_1 is a diameter of circle CC, then line L2L_2 is not a chord of circle CC.

Options

A

STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is a correct explanation for STATEMENT-1

B

STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is NOT a correct explanation for STATEMENT-1

C

STATEMENT-1 is True, STATEMENT-2 is False

Correct
D

STATEMENT-1 is False, STATEMENT-2 is True

Step-by-Step Solution

To determine the correctness of STATEMENT-1 and STATEMENT-2, we analyze the given equations of the lines and the circle step-by-step.

1. Circle Properties

The equation of the given circle is:
C:x2+y2+6x−10y+30=0C : x^2 + y^2 + 6x - 10y + 30 = 0

Comparing this with the general form x2+y2+2gx+2fy+c=0x^2 + y^2 + 2gx + 2fy + c = 0, we get:

  • Center, O=(−g,−f)=(−3,5)O = (-g, -f) = (-3, 5)
  • Radius, R=g2+f2−c=(−3)2+52−30=9+25−30=4=2R = \sqrt{g^2 + f^2 - c} = \sqrt{(-3)^2 + 5^2 - 30} = \sqrt{9 + 25 - 30} = \sqrt{4} = 2

2. Analysis of STATEMENT-1

The line L1L_1 is given by:
L1:2x+3y+p−3=0L_1 : 2x + 3y + p - 3 = 0

For L1L_1 to be a chord of circle CC, the perpendicular distance d1d_1 from the center O(−3,5)O(-3, 5) to the line L1L_1 must be less than the radius RR:
d1=∣2(−3)+3(5)+p−3∣22+32<2d_1 = \frac{|2(-3) + 3(5) + p - 3|}{\sqrt{2^2 + 3^2}} < 2
  ⟹  ∣p+6∣13<2  ⟹  ∣p+6∣<213\implies \frac{|p + 6|}{\sqrt{13}} < 2 \implies |p + 6| < 2\sqrt{13}
  ⟹  p∈(−6−213,−6+213)\implies p \in (-6 - 2\sqrt{13}, -6 + 2\sqrt{13})

Since 213≈7.212\sqrt{13} \approx 7.21, the range of pp for L1L_1 to be a chord is approximately (−13.21,1.21)(-13.21, 1.21).

For L2:2x+3y+p+3=0L_2 : 2x + 3y + p + 3 = 0 to be a diameter of circle CC, it must pass through the center O(−3,5)O(-3, 5):
2(−3)+3(5)+p+3=0  ⟹  p+12=0  ⟹  p=−122(-3) + 3(5) + p + 3 = 0 \implies p + 12 = 0 \implies p = -12

Thus, L2L_2 is a diameter only when p=−12p = -12. For any other value of pp in the range (−13.21,1.21)(-13.21, 1.21) (for instance, p=0p = 0), L1L_1 is a chord, but L2L_2 is not a diameter.

Therefore, STATEMENT-1 ("If line L1L_1 is a chord of circle CC, then line L2L_2 is not always a diameter of circle CC") is TRUE.


3. Analysis of STATEMENT-2

For line L1L_1 to be a diameter of circle CC, it must pass through the center O(−3,5)O(-3, 5):
2(−3)+3(5)+p−3=0  ⟹  p+6=0  ⟹  p=−62(-3) + 3(5) + p - 3 = 0 \implies p + 6 = 0 \implies p = -6

Substituting p=−6p = -6 into the equation for L2L_2:
L2:2x+3y+(−6)+3=0  ⟹  2x+3y−3=0L_2 : 2x + 3y + (-6) + 3 = 0 \implies 2x + 3y - 3 = 0

Now, let's find the perpendicular distance d2d_2 from the center O(−3,5)O(-3, 5) to L2L_2:
d2=∣2(−3)+3(5)−3∣22+32=∣−6+15−3∣13=613d_2 = \frac{|2(-3) + 3(5) - 3|}{\sqrt{2^2 + 3^2}} = \frac{|-6 + 15 - 3|}{\sqrt{13}} = \frac{6}{\sqrt{13}}

Comparing d2d_2 with the radius R=2R = 2:
d22=3613≈2.77d_2^2 = \frac{36}{13} \approx 2.77
R2=4R^2 = 4

Since d22<R2  ⟹  d2<Rd_2^2 < R^2 \implies d_2 < R, the line L2L_2 intersects the circle at two distinct points, meaning L2L_2 is a chord of circle CC.

Therefore, STATEMENT-2 ("If line L1L_1 is a diameter of circle CC, then line L2L_2 is not a chord of circle CC") is FALSE.


Conclusion

  • STATEMENT-1 is True
  • STATEMENT-2 is False

Thus, the correct choice is Option C.