- #1
Math10
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Homework Statement
Find a second solution y2 for x^2*y"+xy'-y=0; y1=x that isn't a constant multiple of the solution y1.
Homework Equations
None.
The Attempt at a Solution
Here's my work:
I divided by x^2,
y"+(1/x)y'-(1/x^2)y=0
P(x)=1/x and Q(x)=-1/x^2
Let y(x)=v(x)*x
y'(x)=v'(x)*x+v(x)
(1/x)y'(x)=v'(x)+v(x)/x
y"(x)=v'(x)+v"(x)*x+v'(x)=xv"(x)+2v'(x)
xv"(x)+2v'(x)+v'(x)+v(x)/x-v(x)*x/(x^2)=0
xv"(x)+3v'(x)=0
Let w=v'
w'=v"
xw'+3w=0
w'=-3w/x
dw/dx=-3w/x
dw/w=-3/x dx
integrate
ln abs(w)=-3ln abs(x)+C
Don't count C, the constant.
w=1/x^3
w=v'=1/x^3
dv/dx=1/x^2
don't count c, the constant.
v=-1/2x^2
y=v*x
y=-1/2x^2*x=-1/2x
But the answer in the book is y2=1/x. I got y=-1/2x, which answer is right?