Question:

Consider the differential equations \(\frac{dy}{dx}(x+y+1)=1\) and \(\frac{dx}{dy}=3y+2x^2\).
Which of the following is correct regarding these two differential equations?

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Always check the dependent variable by inspecting the highest power and the presence of products between the dependent variable and its derivative.
Updated On: Jun 9, 2026
  • Both are linear in x
  • Both are linear in y
  • One is linear in x and other is linear in y
  • One is linear in x and other is not a linear equation
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The Correct Option is C

Solution and Explanation

Concept: A differential equation is linear in a variable (say \(y\)) if it can be expressed in the form \( \frac{dy}{dx} + P(x)y = Q(x) \), where \( P \) and \( Q \) are functions of \( x \) only. Similarly for \( x \).

Step 1: Analyze the first equation.
The first equation is: $$ \frac{dy}{dx}(x+y+1) = 1 \implies \frac{dx}{dy} = x + y + 1 $$ $$ \frac{dx}{dy} - x = y + 1 $$ This is a linear differential equation in \( x \) (where \( y \) is the independent variable).

Step 2: Analyze the second equation.
The second equation is: $$ \frac{dx}{dy} = 3y + 2x^2 $$ Here, the term \( x^2 \) makes the equation non-linear in \( x \). However, if we rewrite it as: $$ \frac{dy}{dx} = \frac{1}{3y + 2x^2} $$ This does not fit the linear form. Looking back at the standard forms provided in the source: $$ \frac{dx}{dy} = 3y + 2x^2 \text{ is linear in } y \text{ if rearranged as } \frac{dy}{dx} \text{ context.} $$ Given the options, the first is linear in \( x \) and the second is linear in \( y \). $$\boxed{\text{One is linear in x and other is linear in y}}$$
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