The question is:
The indicated function y1(x) is a solution of the associated homogeneous equation. Use the method of reduction of order to find a second solution y2(x) of the homogeneous equation
x²y'' - 7xy' + 16y = 0; y1 = x^4
Answer:
The second solution y2 is
A(x^4)lnx
Step-by-step explanation:
Given the homogeneous differential equation
x²y'' - 7xy' + 16y = 0
And a solution: y1 = x^4
We need to find a second solution y2 using the method of reduction of order.
Let y2 = uy1
=> y2 = ux^4
Since y2 is also a solution to the differential equation, it also satisfies it.
Differentiate y2 twice in succession with respect to x, to obtain y2' and y2'' and substitute the resulting values into the original differential equation.
y2' = u'. x^4 + u. 4x³
y2'' = u''. x^4 + u'. 4x³ + u'. 4x³ + u. 12x²
= u''. x^4 + u'. 8x³ + u. 12x²
Now, using these values in the original equation,
x²(u''. x^4 + u'. 8x³ + u. 12x²) - 7x(u'. x^4 + u. 4x³)+ 16(ux^4) = 0
x^6u'' + 8x^5u' + 12x^4u - 7x^5u' - 28x^4u + 16x^4u = 0
x^6u'' + x^5u' = 0
xu'' = -u'
Let w = u'
Then w' = u''
So
xw' = -w
w'/w = -1/x
Integrating both sides
lnw = -lnx + C
w = Ae^(-lnx) (where A = e^C)
w = A/x
But w = u'
So,
u' = A/x
Integrating this
u = Alnx
Since
y2 = uy1
We have
y2 = (Alnx)x^4 = (Ax^4)lnx
Therefore, the second solution y2 is
A(x^4)lnx
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