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Class 12 Continuity And Differentiability · Assertion Reason1 Marksassertion_reason

Class 12 Maths · Continuity And Differentiability · Assertion Reason #33

Assertion: For y=(sin x+cos x)², y′(π/4)=0. Reason: The second derivative is the derivative of the first derivative.

(A) Both A and R are true, and R correctly explains A.
(B) Both A and R are true, but R does not correctly explain A.
(C) A is true, but R is false.
(D) A is false, but R is true.

✅ Step-by-Step Solution

Final Answer: Option (B): Both A and R are true, but R does not correctly explain A.

Differentiate to get y′=2(sin x+cos x)(cos x−sin x)=2cos2x, which is 0 at π/4. The reason is true but concerns the second derivative and does not explain this value.

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