JEE Advanced · Mathematics · 12. Circle
Two parallel chords of a circle of radius 2 are at a distance \(\sqrt{3}+1\) apart. If the chords subtend at the centre, angles of \(\frac{\pi}{k}\) and \(\frac{2 \pi}{k}\), where \(k>0\), then the value of \([k]\) is
[Note : \([k]\) denotes the largest integer less than or equal to \(k\) ]
- A 3
- B 5
- C 7
- D 9
Answer & Solution
Correct Answer
(A) 3
Step-by-step Solution
Detailed explanation
Let \(\theta=\frac{\pi}{2 k}\)

\[
\begin{aligned}
& \cos \theta=\frac{x}{2} \\
& \Rightarrow \quad \cos 2 \theta=\frac{\sqrt{3}+1-x}{2} \\
& \Rightarrow 2 \cos ^2 \theta-1=\frac{\sqrt{3}+1-x}{2} \\
& \Rightarrow 2\left(\frac{x^2}{4}\right)-1=\frac{\sqrt{3}+1-x}{2} \\
& \Rightarrow \quad x^2+x-3-\sqrt{3}=0 \\
& \Rightarrow \quad x=\frac{-1 \pm \sqrt{1+12+4 \sqrt{3}}}{2} \\
& =\frac{-1 \pm \sqrt{13+4 \sqrt{3}}}{2} \\
& =\frac{-1+2 \sqrt{3}+1}{2}=\sqrt{3} \\
& \therefore \quad \cos \theta=\frac{\sqrt{3}}{2} \Rightarrow \theta=\frac{\pi}{6} \\
& \therefore \quad \text { Required angle }=\frac{\pi}{k}=2 \theta=\frac{\pi}{3} \\
& \Rightarrow \quad k=3 \\
&
\end{aligned}
\]

\[
\begin{aligned}
& \cos \theta=\frac{x}{2} \\
& \Rightarrow \quad \cos 2 \theta=\frac{\sqrt{3}+1-x}{2} \\
& \Rightarrow 2 \cos ^2 \theta-1=\frac{\sqrt{3}+1-x}{2} \\
& \Rightarrow 2\left(\frac{x^2}{4}\right)-1=\frac{\sqrt{3}+1-x}{2} \\
& \Rightarrow \quad x^2+x-3-\sqrt{3}=0 \\
& \Rightarrow \quad x=\frac{-1 \pm \sqrt{1+12+4 \sqrt{3}}}{2} \\
& =\frac{-1 \pm \sqrt{13+4 \sqrt{3}}}{2} \\
& =\frac{-1+2 \sqrt{3}+1}{2}=\sqrt{3} \\
& \therefore \quad \cos \theta=\frac{\sqrt{3}}{2} \Rightarrow \theta=\frac{\pi}{6} \\
& \therefore \quad \text { Required angle }=\frac{\pi}{k}=2 \theta=\frac{\pi}{3} \\
& \Rightarrow \quad k=3 \\
&
\end{aligned}
\]
See the Complete Solution
Get step-by-step explanations for this and 2.5 Lakh+ more JEE, NEET & CET questions.
- Unlock all solutions
- Practice the full chapter
- Track accuracy across PYQs
4.8 rated on Google Play · 14,000+ reviews
More questions from Mathematics
- The product of all positive real values of satisfying the equation isJEE Advanced 2022 Medium
- Let \(P(3,2,6)\) be a point in space and \(Q\) be a point on the line \(\mathbf{r}=(\hat{\mathbf{i}}-\hat{\mathbf{j}}+2 \hat{\mathbf{k}})+\mu(-3 \hat{\mathbf{i}}+\hat{\mathbf{j}}+5 \hat{\mathbf{k}})\).
Then, the value of \(\mu\) for which the vector \(\mathbf{P Q}\) is parallel to the plane \(x-4 y+3 z=1\) isJEE Advanced 2009 Medium -

If \(n(X)={ }^m C_6\), then the value of \(m\) isJEE Advanced 2024 Medium - \[
\text { Let } M \text { be a } 3 \times 3 \text { matrix satisfying }
\]
\[
M\left[\begin{array}{l}
0 \\
1 \\
0
\end{array}\right]=\left[\begin{array}{c}
-1 \\
2 \\
3
\end{array}\right], M\left[\begin{array}{c}
1 \\
-1 \\
0
\end{array}\right]=\left[\begin{array}{c}
1 \\
1 \\
-1
\end{array}\right] \text { and } M\left[\begin{array}{l}
1 \\
1 \\
1
\end{array}\right]=\left[\begin{array}{c}
0 \\
0 \\
12
\end{array}\right]
\]
Then, the sum of the diagonal entries of \(M\) isJEE Advanced 2011 Easy - Let be a function. We say that has:
PROPERTY if exists and is finite, and
PROPERTY if exists and is finite.
Then which of the following options is/are correct?JEE Advanced 2019 Medium - Paragraph:
Let \(a, r, s, t\) be nonzero real numbers. Let \(P\left(a t^{2}, 2 a t\right), Q, R\left(a r^{2}, 2 a r\right)\) and \(S\left(a s^{2}, 2 a s\right)\) be distinct points on the parabola \(y^{2}=4 a x\). Suppose that \(P Q\) is the focal chord and lines \(Q R\) and \(P K\) are parallel, where \(K\) is the point \((2 a, 0)\).
Question:
The value of \(r\) isJEE Advanced 2014 Medium
More PYQs from JEE Advanced
- Two balls, having linear momenta \(\overrightarrow{\mathbf{p}}_1=p \hat{\mathbf{i}}\) and \(\overrightarrow{\mathbf{p}}_2=-p \hat{\mathbf{i}}\), undergo a collision in free space. There is no external force acting on the balls. Let \(\overrightarrow{\mathbf{p}}_1^{\prime}\) and \(\overrightarrow{\mathbf{p}}_2^{\prime}\) be their final momenta. The following option(s) is/are NOT ALLOWED for any non-zero value of \(p, a_1, a_2, b_1, b_2, c_1\) and \(c_2\)JEE Advanced 2008 Easy
- A block hangs vertically at the bottom end of a uniform rope of constant mass per unit length. The top end of the rope is attached to a fixed rigid support at O. A transverse wave pulse (Pulse 1) of wavelength is produced at point O on the rope. The pulse takes time to reach point A. If the wave pulse of wavelength is produced at point A (Pulse 2) without disturbing the position of M it takes time to reach point O. Which of the following options is/are correct?
JEE Advanced 2017 Medium - A person blows into open-end of a long pipe. As a result, a high pressure pulse of air travels down the pipe.
When this pulse reaches the other end of the pipe,JEE Advanced 2012 Hard - Let \(\frac{\pi}{2} < x < \pi\) be such that \(\cot x=\frac{-5}{\sqrt{11}}\). Then \(\left(\sin \frac{11 x}{2}\right)(\sin 6 x-\cos 6 x)+\left(\cos \frac{11 x}{2}\right)(\sin 6 x+\cos 6 x)\) is equal toJEE Advanced 2024 Hard
- Paragraph:
The figure shows a circular loop of radius \(a\) with two long parallel wires (numbered \(1\) and \(2\) ) all in the plane of the paper. The distance of each wire from the centre of the loop is \(d\). The loop and the wires are carrying the same current \(I\). The current in the loop is in the counterclockwise direction if seen from above.
Question:
Consider \(d \gg a\), and the loop is rotated about its diameter parallel to the wires by \(30^{\circ}\) from the position shown in the figure. If the currents in the wires are in the opposite directions, the torque on the loop at its new position will be (assume that the net field due to the wires is constant over the loop)JEE Advanced 2014 Hard - Sulfide ores are common for the metalsJEE Advanced 2013 Medium