Q.41 The solution to
dy/dx + y cot x = cosec x
is
- y = (c + x) cot x
- y = (c + x) cosec x
- y = (c + x) cosec x cot x
- y = (c + x) cosec x / cot x
Step-by-Step Solution
Step 1: Identify the Standard Form
The given equation is a first-order linear differential equation of the form:
dy/dx + P(x)y = Q(x)
Here,
P(x) = cot x
Q(x) = cosec x
Step 2: Find the Integrating Factor (IF)
Integrating Factor (IF) = e∫P(x) dx
IF = e∫cot x dx
∫cot x dx = ln(sin x)
IF = eln(sin x) = sin x
Step 3: Multiply the Equation by IF
sin x · dy/dx + y sin x cot x = sin x cosec x
Since:
sin x cot x = cos x
sin x cosec x = 1
The equation becomes:
d/dx (y sin x) = 1
Step 4: Integrate Both Sides
∫ d/dx (y sin x) dx = ∫ 1 dx
y sin x = x + c
Step 5: Solve for y
y = (x + c) / sin x
y = (c + x) cosec x
Correct Answer
Option (B):
y = (c + x) cosec x
Conclusion
The solution of the differential equation dy/dx + y cot x = cosec x using the integrating factor method is:
y = (c + x) cosec x


