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Let CC be the circle x2+y2+4x−6y−3=0x^2 + y^2 + 4x - 6y - 3 = 0 and LL be the locus of the point of intersection of a pair of tangents to CC with the angle between the two tangents equal to 60°60°. Then, the point at which LL touches the line x=6x = 6 is

Solution

✅ Correct Option: 4

Given: x2+y2+4x−6y−3=0x^2 + y^2 + 4x - 6y - 3 = 0

The standard form of a circle is (x−h)2+(y−k)2=r2(x-h)^2 + (y-k)^2 = r^2, where (h,k)(h,k) is the center and rr is the radius.

(x2+4x)+(y2−6y)−3=0(x^2 + 4x) + (y^2 - 6y) - 3 = 0

For x: x2+4x+4=(x+2)2x^2 + 4x + 4 = (x+2)^2 (add and subtract 4)

For y: y2−6y+9=(y−3)2y^2 - 6y + 9 = (y-3)^2 (add and subtract 9)

(x+2)2+(y−3)2−4−9−3=0(x+2)^2 + (y-3)^2 - 4 - 9 - 3 = 0

(x+2)2+(y−3)2=16(x+2)^2 + (y-3)^2 = 16

Center =(−2,3)= (-2, 3) and Radius =16=4= \sqrt{16} = 4


When two tangents are drawn from an external point P to a circle, the tangents have equal length and the angle between the center-to-point line and each tangent is the same.

If the angle between the two tangents is 60°60°, then each tangent makes an angle of 30°30° with the line joining the external point to the center.


In the right triangle formed by:

A == point of tangency

C == center of circle (−2,3)(-2, 3)

P == external point

We have:

∠CAP=90°\angle CAP = 90° (radius perpendicular to tangent)

∠ACP=30°\angle ACP = 30° (half of the 60°60° angle between tangents)

AC=4AC = 4 (radius)

Using trigonometry in right triangle ACP:

sin⁡(30°)=ACCP=4CP\sin(30°) = \tfrac{AC}{CP} = \tfrac{4}{CP}

Since sin⁡(30°)=12\sin(30°) = \tfrac{1}{2}:

12=4CP\tfrac{1}{2} = \tfrac{4}{CP}

Therefore: CP=8CP = 8


The locus L consists of all points P that are at distance 8 from the center (−2,3)(-2, 3).

Locus equation: (x+2)2+(y−3)2=64(x+2)^2 + (y-3)^2 = 64


We substitute x=6x = 6 into the locus equation:

(6+2)2+(y−3)2=64(6+2)^2 + (y-3)^2 = 64

64+(y−3)2=6464 + (y-3)^2 = 64

(y−3)2=0(y-3)^2 = 0

y=3y = 3


The point where L touches the line x=6x = 6 is (6,3)(6, 3).

The point (6,3)(6, 3) is exactly 8 units away from the center (−2,3)(-2, 3), confirming our geometric analysis. From this point, tangents drawn to the circle will indeed make a 60°60° angle with each other.

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