Mathematics · Trigonometry Ratios and Identities

JEE Main 2024 — 27 January, Shift 1 — Question 25

Let the set of all a∈Ra \in R such that the equation cos⁡2x+asin⁡x=2a−7\cos 2 x+a \sin x=2 a-7 has a solution be [p,q][p, q] and r=tan⁡9∘−tan⁡27∘−1cot⁡63∘+tan⁡81∘r=\tan 9^{\circ}-\tan 27^{\circ}-\frac{1}{\cot 63^{\circ}}+\tan 81^{\circ}, then pqr is equal to

Answer: 48

Numerical answer — enter this value.

Step-by-step solution

cos⁡2x+a⋅sin⁡x=2a−7\cos 2 \mathrm{x}+\mathrm{a} \cdot \sin \mathrm{x}=2 \mathrm{a}-7

a(sin⁡x−2)=2(sin⁡x−2)(sin⁡x+2)a(\sin x-2)=2(\sin x-2)(\sin x+2)

sin⁡x=2,a=2(sin⁡x+2) \sin x=2, a=2(\sin x+2)

⇒a∈[2,6]\Rightarrow a \in[2,6]

p=2,q=6p=2 , q=6

r=tan⁡9∘+cot⁡9∘−tan⁡27−cot⁡27r=\tan 9^{\circ}+\cot 9^{\circ}-\tan 27-\cot 27

r=1sin⁡9⋅cos⁡9−1sin⁡27⋅cos⁡27r=\frac{1}{\sin 9 \cdot \cos 9}-\frac{1}{\sin 27 \cdot \cos 27}

=2[45−1−45+1]=2\left[\frac{4}{\sqrt{5}-1}-\frac{4}{\sqrt{5}+1}\right]

r=4r=4

p⋅q⋅r=2×6×4=48p \cdot q \cdot r=2 \times 6 \times 4=48

Answer key and solution verified before publishing.

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Exam
JEE Main 2024
Subject
Mathematics
Chapter
Trigonometry Ratios and Identities
Topic
Trigonometric Ratios of Multiples and Submultiples of angles
Let the set of all a in R such that the equation cos 2 x+a sin x=2… | JEE Main 2024 PYQ with Solution · DhiX AI