Target Exam

CUET

Subject

-- Mathematics - Section A

Chapter

Differential Equations

Question:

Match List-I with List-II

List-I

Differential Equation

List-II

Order and degree of differential equation

(A) $\frac{d^2y}{dx^2}+2(\frac{dy}{dx})^2=e^{\frac{dy}{dx}}+1$

(I) Order = 1, Degree = 2

(B) $(\frac{d^2y}{dx^2})^2+4(\frac{dy}{dx})^3=e^y – 1$

(II) Order = 2, Degree = 1

(C) $3 (\frac{dy}{dx})+4y+e^y=\frac{dy}{dx}$

(III) Order = 2, Degree = 2

(D) $\frac{d^2y}{dx^2}+3(\frac{dy}{dx})= (e^y+\frac{dy}{dx})^2$

(IV) Order = 2, Degree = Not defined

Choose the correct answer from the options given below:

Options:

(A)-(I), (B)-(II), (C)-(III), (D)-(IV)

(A)-(II), (B)-(III), (C)-(IV), (D)-(I)

(A)-(IV), (B)-(III), (C)-(I), (D)-(II)

(A)-(IV), (B)-(III), (C)-(II), (D)-(I)

Correct Answer:

(A)-(IV), (B)-(III), (C)-(I), (D)-(II)

Explanation:

The correct answer is Option (3) → (A)-(IV), (B)-(III), (C)-(I), (D)-(II)

Given differential equations and to find order and degree:

(A) \(\frac{d^2y}{dx^2} + 2 \left(\frac{dy}{dx}\right)^2 = e^{\frac{dy}{dx}} + 1\)

- Order is highest derivative: \(\frac{d^2y}{dx^2}\) ⇒ Order = 2

- Degree is the power of highest order derivative after removing radicals and fractions of derivatives. Here, \(\frac{d^2y}{dx^2}\) is to the power 1 but RHS has exponential of \(\frac{dy}{dx}\), which is not a polynomial expression in derivatives ⇒ Degree is not defined.

(B) \(\left(\frac{d^2y}{dx^2}\right)^2 + 4 \left(\frac{dy}{dx}\right)^3 = e^y - 1\)

- Highest order derivative is \(\frac{d^2y}{dx^2}\) squared ⇒ Order = 2

- Degree is the power of highest order derivative after simplification ⇒ Degree = 2

(C) \(3 \frac{dy}{dx} + 4y + e^y = \frac{dy}{dx}\)

- Highest order derivative is \(\frac{dy}{dx}\) ⇒ Order = 1

- Degree is the power of \(\frac{dy}{dx}\) after simplification. Rearranging: \(3 \frac{dy}{dx} - \frac{dy}{dx} = -4y - e^y \Rightarrow 2 \frac{dy}{dx} = \ldots\), degree of \(\frac{dy}{dx}\) is 1, no powers, but the term \(e^y\) is not involving derivative.

But since \(\frac{dy}{dx}\) appears to power 1, degree = 1

(D) \(\frac{d^2y}{dx^2} + 3 \frac{dy}{dx} = (e^y + \frac{dy}{dx})^2\)

- Highest order derivative is \(\frac{d^2y}{dx^2}\) ⇒ Order = 2

- Degree is power of \(\frac{d^2y}{dx^2}\) which is 1 (since it is not raised to any power)

- The RHS is a square of expression involving first derivative, but highest order derivative is second derivative raised to 1 only ⇒ Degree = 1

Matching:

  • (A) → (IV) Order = 2, Degree = Not defined
  • (B) → (III) Order = 2, Degree = 2
  • (C) → (I) Order = 1, Degree = 1
  • (D) → (II) Order = 2, Degree = 1