Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
JEE Main
Exam
JEE Main
Subject
Mathematics
Chapter
Trigonometric Ratios & Identities

JEE Main · Mathematics · Trigonometric Ratios & Identities

Let S = \ θ ∈ (0, (π)/(2)) : ∑_ m=1 ^ 6 (θ + (m-1)(π)/(4)) (θ +...

Let S={θ∈(0,π2):∑m=16csc⁡(θ+(m−1)π4)csc⁡(θ+mπ4)=42}S = \left\{ \theta \in \left(0, \dfrac{\pi}{2}\right) : \sum_{m=1}^{6} \csc\left(\theta + (m-1)\dfrac{\pi}{4}\right) \csc\left(\theta + \dfrac{m\pi}{4}\right) = 4\sqrt{2} \right\}. If α\alpha and β\beta are the largest and smallest elements of SS respectively, then the value of α−β\alpha - \beta is

Options

  1. Aπ3\dfrac{\pi}{3}
  2. Bπ12\dfrac{\pi}{12}
  3. C5π12\dfrac{5\pi}{12}
  4. Dπ2\dfrac{\pi}{2}

Correct answer

A. π3\dfrac{\pi}{3}

Step-by-step solution

Let the given sum be EE. We can write the product of cosecants as:

E=∑m=161sin⁡(θ+(m−1)π4)sin⁡(θ+mπ4)E = \sum_{m=1}^{6} \dfrac{1}{\sin\left(\theta + (m-1)\dfrac{\pi}{4}\right) \sin\left(\theta + \dfrac{m\pi}{4}\right)}

Multiplying and dividing by sin⁡(π4)=12\sin\left(\dfrac{\pi}{4}\right) = \dfrac{1}{\sqrt{2}}, we get:

E=2∑m=16sin⁡((θ+mπ4)−(θ+(m−1)π4))sin⁡(θ+(m−1)π4)sin⁡(θ+mπ4)E = \sqrt{2} \sum_{m=1}^{6} \dfrac{\sin\left(\left(\theta + \dfrac{m\pi}{4}\right) - \left(\theta + (m-1)\dfrac{\pi}{4}\right)\right)}{\sin\left(\theta + (m-1)\dfrac{\pi}{4}\right) \sin\left(\theta + \dfrac{m\pi}{4}\right)}

E=2∑m=16[cot⁡(θ+(m−1)π4)−cot⁡(θ+mπ4)]E = \sqrt{2} \sum_{m=1}^{6} \left[ \cot\left(\theta + (m-1)\dfrac{\pi}{4}\right) - \cot\left(\theta + \dfrac{m\pi}{4}\right) \right]

This is a telescoping sum. Expanding the terms:

E=2[(cot⁡θ−cot⁡(θ+π4))+(cot⁡(θ+π4)−cot⁡(θ+2π4))+⋯+(cot⁡(θ+5π4)−cot⁡(θ+6π4))]E = \sqrt{2} \left[ \left(\cot\theta - \cot\left(\theta + \dfrac{\pi}{4}\right)\right) + \left(\cot\left(\theta + \dfrac{\pi}{4}\right) - \cot\left(\theta + \dfrac{2\pi}{4}\right)\right) + \dots + \left(\cot\left(\theta + \dfrac{5\pi}{4}\right) - \cot\left(\theta + \dfrac{6\pi}{4}\right)\right) \right]

E=2[cot⁡θ−cot⁡(θ+3π2)]E = \sqrt{2} \left[ \cot\theta - \cot\left(\theta + \dfrac{3\pi}{2}\right) \right]

Using the allied angle identity cot⁡(θ+3π2)=−tan⁡θ\cot\left(\theta + \dfrac{3\pi}{2}\right) = -\tan\theta, we have:

E=2(cot⁡θ+tan⁡θ)=2(cos⁡θsin⁡θ+sin⁡θcos⁡θ)=2sin⁡θcos⁡θ=22sin⁡(2θ)E = \sqrt{2} (\cot\theta + \tan\theta) = \sqrt{2} \left( \dfrac{\cos\theta}{\sin\theta} + \dfrac{\sin\theta}{\cos\theta} \right) = \dfrac{\sqrt{2}}{\sin\theta \cos\theta} = \dfrac{2\sqrt{2}}{\sin(2\theta)}

We are given that E=42E = 4\sqrt{2}.

22sin⁡(2θ)=42⇒sin⁡(2θ)=12\dfrac{2\sqrt{2}}{\sin(2\theta)} = 4\sqrt{2} \Rightarrow \sin(2\theta) = \dfrac{1}{2}

Since θ∈(0,π2)\theta \in \left(0, \dfrac{\pi}{2}\right), we have 2θ∈(0,π)2\theta \in (0, \pi). The solutions for 2θ2\theta are π6\dfrac{\pi}{6} and 5π6\dfrac{5\pi}{6}.

Thus, θ=π12,5π12\theta = \dfrac{\pi}{12}, \dfrac{5\pi}{12}.

The largest element is α=5π12\alpha = \dfrac{5\pi}{12} and the smallest is β=π12\beta = \dfrac{\pi}{12}.

The absolute difference is α−β=5π12−π12=4π12=π3\alpha - \beta = \dfrac{5\pi}{12} - \dfrac{\pi}{12} = \dfrac{4\pi}{12} = \dfrac{\pi}{3}.

Answer: π3\dfrac{\pi}{3}
Practice Trigonometric Ratios & Identities on Quantrex Academy →

More from Trigonometric Ratios & Identities

Let α = (1 - 2 ((π)/(11)))(1 - 2 ((3π)/(11)))(1 - 2 ((9π)/(11)))(1 - 2 ((27π)/(11)))(1… JEE Advanced 2026If A = ( 3^∘)/( 9^∘) + ( 9^∘)/( 27^∘) + ( 27^∘)/( 81^∘) and B = 81^∘ - 3^∘ , then (B)/(A)… JEE Main 2026Let P = \ θ ∈ [0, 4π] : ^2θ ≠ 1\ and S = \ a ∈ ℤ : 2( ^8θ - ^8θ) 2θ = a^2, θ ∈ P\ . Then… JEE Main 2026If ((π)/(18)) ((5π)/(18)) ((7π)/(18)) = K , then the value of ((10Kπ)/(3)) is : JEE Main 2026If (A-B) A + ^ 2 C ^ 2 ~A =1, ~A, ~B, C ∈(0, (π)/(2)) , then JEE Main 2026If x=(5)/(12) for some x ∈(π, (3 π)/(2)) , then 7 x( (13 x)/(2)+ (13 x)/(2))+ 7 x( (13… JEE Main 2026The value of 3 cosec 20^ ∘ - 20^ ∘ 20^ ∘ 40^ ∘ 60^ ∘ 80^ ∘ is equal to JEE Main 2026The least value of ( ^ 2 θ-6 θ θ+3 ^ 2 θ+2) is JEE Main 2026Let (π)/(2) ((15 θ)/(2))( 8 θ+ 8 θ)+ ((15 θ)/(2))( 8 θ- 8 θ) is equal to JEE Main 2026Let α and β respectively be the maximum and the minimum values of the function f(θ)=4( ^… JEE Main 2026Let (α+β)=-(1)/(10) and (α-β)=(3)/(8) , where 0<α<(π)/(3) and 0<β<(π)/(4) . If 2 α= 3(1-r… JEE Main 2026If ^ 2 48^ ∘ - ^ 2 12^ ∘ ^ 2 24^ ∘ - ^ 2 6^ ∘ = α+β 5 2 , where α, β ∈ ℕ , then α+β is… JEE Main 2026The value of cosec 10^ ∘ - 3 10^ ∘ is equal to : JEE Main 2026Let α= 1 60^ ∘ 61^ ∘ + 1 62^ ∘ 63^ ∘ +…+ 1 118^ ∘ 119^ ∘ Then the value of ( cosec 1^ ∘ α… JEE Advanced 2025If x+ ^2 x=1, x ∈(0, (π)/(2)) , then ( ^ 12 x+ ^ 12 x)+3( ^ 10 x+ ^ 10 x+ ^8 x+ ^8 x)+(… JEE Main 2025If ∑_ r=1 ^ 13 \ (1)/( ((π)/(4)+(r-1) (π)/(6)) ((π)/(4)+(r π)/(6)))\ =a 3 +b, a, b ∈ Z… JEE Main 2025 Full Trigonometric Ratios & Identities list Trigonometric Ratios & Identities JEE Maths PYQsJEE Mathematics PYQs All JEE Main PYQs