Question Details

An ordinary differential equation is given below.


x 2 d 2 y d x 2 = 6 y



Considering a and b as arbitrary constants, the general solution of the equation is

Options

A

y(x) = ax3 + b/x2

B

y(x) = ax2 + b/x3

C

y(x) = ax2 +blnx

D

y(x) = ax3 +blnx

Show Answer

Correct Answer :

Option A

y(x) = ax3 + b/x2

Solution :

The correct option is: y(x) = ax3 + b/x2

Step-by-step Explanation:

The given ordinary differential equation is a second-order Euler-Cauchy (or Cauchy-Euler) equation:
x2 d2y dx2 = 6 y
We can rewrite this in standard Euler-Cauchy form as:
x2 d2y dx2 - 6 y = 0

To solve this differential equation, we assume a solution of the form:
y = xm
Differentiating y twice with respect to x gives:
dy dx = m xm-1
d2y dx2 = m ( m - 1 ) xm-2

Substituting these expressions back into the original differential equation, we get:
x2 [ m ( m - 1 ) xm-2 ] - 6 xm = 0
Simplifying the term x2xm-2=xm, we obtain:
m ( m - 1 ) xm - 6 xm = 0
Factoring out xm (since xm0 for non-trivial solutions):
[ m ( m - 1 ) - 6 ] xm = 0
This yields the characteristic (or auxiliary) equation:
m2 - m - 6 = 0

To find the roots of this quadratic equation, we factor it:
( m - 3 ) ( m + 2 ) = 0
Solving for m gives:
m1 = 3 and m2 = - 2

Since the roots are real and distinct, the general solution of the differential equation is a linear combination of the two independent solutions, x3 and x-2:
y ( x ) = a x3 + b x-2
which can be written as:
y ( x ) = a x3 + b x2
where a and b are arbitrary constants.

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