NCERT Class 12 · Ch 6 Exercise 6.2 · Q12
NCERT Class 12 Maths · Chapter 6 Applications Of Derivatives · Exercise 6.2 Question 12
Which are decreasing on (0,π/2): (A) cos x, (B) cos 2x, (C) cos 3x, (D) tan x?
💡 Concept Hints
- Identify the domain and the inner and outer functions, or the relevant one-sided limits.
- Apply the appropriate differentiation or limit rule, keep all chain factors, and check exceptional points.
✅ Step-by-Step Solution
Final Answer: A and B.
- The derivatives −sin x and −2sin 2x are strictly negative throughout the interval.
- The derivative −3sin 3x changes sign at π/3, while sec²x>0 for tan x. Thus C and D fail.
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