Q66.If 5tan2𝑥- cos2𝑥= 2cos 2𝑥+ 9, then the value of cos4𝑥 is 3 1 (1) - (2) 5 3 2 7 (3) (4) - 9 9
What This Question Tests
The question requires transforming a trigonometric equation using double angle identities and then solving a quadratic equation for cos(2x) to find cos(4x). Note: A direct calculation leads to irrational roots for cos(2x), making the options inconsistent with the problem statement. However, based on common JEE practices, such questions often have a simple answer, suggesting a potential typo in the problem or options. Assuming a specific option (e.g., cos(4x)=-7/9 implying cos(2x)=±1/3) and working backward also shows inconsistency with the original equation, indicating a flawed problem statement from the source. Given the options, students are expected to perform the substitutions and solve the quadratic. For this analysis, the difficulty is set to Hard due to the discrepancy.
Concepts Tested
Formulas Used
cos(2x) = 2cos²x - 1
tan²x = (1-cos(2x))/(1+cos(2x))
cos(4x) = 2cos²(2x) - 1
📚 NCERT Sections This Tests
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5.28 — How Many Ions Are Produced From The Complex Co(Nh3)6Cl2 In Solution?
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5.28 How many ions are produced from the complex Co(NH3)6Cl2 in solution? (i) 6 (ii) 4 (iii) 3 (iv) 2 139 Coordination Compounds Reprint 2025-26
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📋 Question Details
- Chapter
- Trigonometric Functions & Equations
- Topic
- Trigonometric identities and equations
- Year
- 2017
- Shift
- 02 Apr
- Q Number
- Q66
- Type
- MCQ
- NCERT Ref
- Class 11 Mathematics Ch 3: Trigonometric Functions
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