CUET · MATHS · PYQ PAPER 2025

The edge of a cube is increasing at a rate of \(7 cm / s\). The rate of change of area of the cube when edge of the cube is 3 cm is :

A \(42 cm^2 / s\)
B \(168 cm^2 / s\)
C \(84 cm^2 / s\)
D \(252 cm^2 / s\)

Verified Solution

Answer & Solution

Correct Answer

(D) \(252 cm^2 / s\)

Step-by-step Solution

Detailed explanation

\( A = 6s^2 \) \( \frac{dA}{dt} = 12s \frac{ds}{dt} \) \( \frac{dA}{dt} = 12(3)(7) \) \( \frac{dA}{dt} = 252 \, cm^2 / s \)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

Same subject

Match List-I with List-II

List - I (Differential Equations)	List - II (Degree/Order)
(A) Degree of the differential equation \(\frac{d^3 y}{d x^3}+2 \log x \cdot y=0\)	(I) 3
(B) Order of the differential equation \(\frac{d^4 y}{d x^4}+\left(\frac{d y}{d x}\right)^4+x y=0\)	(II) 2
(C) Degree of the differential equation \(\left(\frac{d^4 y}{d x^4}\right)^2+\left(\frac{d y}{d x}\right)^3+x^2 y=0\)	(III) 1
(D) Order of the differential equation \(\frac{d^3 y}{d x^3}+y\left(\frac{d y}{d x}\right)^3=0\)	(IV) 4

Choose the correct answer from the options given below:

CUET 2025 Hard

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