If $5(\tan^2x-\cos^2x)=2\cos2x+9$, then the value of $\cos4x$ is :

JEE Main 2017 · MathsMultiple choiceSingle correctMediumMulti-step

JEE Main 2 April 2017 (offline), Maths Q88

Question 88 of 90 in this shift, Maths question 28 of 30.

5(\tan^2x-\cos^2x)=2\cos2x+9

, then the value of

\cos4x

is :

(1) $\frac{1}{3}$
(2) $\frac{2}{9}$
(3) $-\frac{7}{9}$ Official answer
(4) $-\frac{3}{5}$

Official answer

Option 3

CBSE answer key (25/04/2017, used for result).

Chapter: Trigonometric Functions
Topic: Trigonometric Identities
Idea tested: Multiple Angle Formulas

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Question text from the official JEE Main paper published by NTA (CBSE ran the 2017 exam); answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.