Question Details

The integrating factor of the differential equation ( x logex ) dy / dx + y = 2 logex is

Options

A

logex

B

x

C

x

D

1 logex

Show Answer

Correct Answer :

Option A

logex

Solution :

The correct option is:
logex

To find the integrating factor of the given differential equation, we first write it in standard linear form. The given differential equation is:
( x logex ) dy dx + y = 2 logex

A first-order linear differential equation is typically written in the standard form:
dy dx + P ( x ) y = Q ( x )

To convert our equation into this standard form, we divide every term by the coefficient of dy dx , which is x logex :
dy dx + 1 x logex y = 2 logex x logex

Comparing this with the standard form, we identify the coefficient function P ( x ) as:
P ( x ) = 1 x logex

The formula for the integrating factor (I.F.) is:
I.F. = e P ( x ) d x

First, we evaluate the integral:
P ( x ) d x = 1 x logex d x

To solve this integral, we can use the substitution method. Let:
u = logex
Differentiating both sides with respect to x gives:
d u = 1 x d x

Substituting these values back into the integral:
1 x logex d x = 1 u d u = loge|u|

Replacing u with its original value logex yields:
P ( x ) d x = loge(logex)

Now we calculate the integrating factor:
I.F. = e loge(logex)

Using the exponential-logarithmic identity e logef ( x ) = f ( x ) , the expression simplifies directly to:
I.F. = logex

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