Class CBSE Class 12 Mathematics Differential Equations Q #657
KNOWLEDGE BASED
UNDERSTAND
1 Marks 2025 AISSCE(Board Exam) MCQ SINGLE
If \(p\) and \(q\) are respectively the order and degree of the differential equation \(\frac{d}{dx}(\frac{dy}{dx})^{3}=0,\) then \((p-q)\) is
(A) 0
(B) 1
(C) 2
(D) 3
Correct Answer: B
Explanation


The given differential equation is:




$\displaystyle \frac{d}{dx}\left(\frac{dy}{dx}\right)^3 = 0$



Step 1: Expand the derivative




$\displaystyle \frac{d}{dx}\left(\frac{dy}{dx}\right)^3 = 3\left(\frac{dy}{dx}\right)^2 \frac{d^2y}{dx^2} = 0$



Step 2: Identify order and degree




  • The highest order derivative is $\dfrac{d^2y}{dx^2}$, so the order is $p = 2$.

  • The equation is a polynomial in derivatives, and the degree of the highest derivative is $1$, so $q = 1$.



Step 3: Compute $(p - q)$




$(p - q) = 2 - 1 = 1$



∴ Final Answer: $(p - q) = 1$


AI Tutor Explanation

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Step-by-Step Solution

The given differential equation is \(\frac{d}{dx}(\frac{dy}{dx})^{3}=0\).

First, we simplify the equation:

\(\frac{d}{dx}(\frac{dy}{dx})^{3} = \frac{d}{dx}((\frac{dy}{dx})^{3}) = 0\)

Differentiating \(\left(\frac{dy}{dx}\right)^3\) with respect to \(x\) gives:

\(3\left(\frac{dy}{dx}\right)^2 \cdot \frac{d^2y}{dx^2} = 0\)

The order of a differential equation is the highest order derivative present in the equation. Here, the highest order derivative is \(\frac{d^2y}{dx^2}\), which is the second derivative. So, the order \(p = 2\).

The degree of a differential equation is the power of the highest order derivative, when the differential equation is expressed in a form where all derivatives are free from radicals and fractions. In this case, the power of \(\frac{d^2y}{dx^2}\) is 1. So, the degree \(q = 1\).

Therefore, \(p - q = 2 - 1 = 1\).

Correct Answer: 1

AI Suggestion: Option B

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Pedagogical Audit
Bloom's Analysis: This is an UNDERSTAND question because the student needs to understand the definitions of order and degree of a differential equation to correctly identify them in the given equation and then perform a simple subtraction.
Knowledge Dimension: CONCEPTUAL
Justification: The question requires understanding the concepts of order and degree of a differential equation, rather than just recalling facts or applying a specific procedure.
Syllabus Audit: In the context of CBSE Class 12, this is classified as KNOWLEDGE. The question directly tests the student's understanding of definitions related to differential equations as covered in the textbook.