Is c1 + c2 x^.5 a Solution of y y'' + (y')^.5 = 0?

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SUMMARY

The discussion confirms that y1(x) = 1 and y2(x) = x^.5 are valid solutions to the differential equation y y'' + (y')^.5 = 0. The Wronskian calculated as 1/(2 sqrt(x)) indicates that these solutions form a fundamental set. However, the expression c1 + c2 x^.5 is not a general solution due to the non-linearity of the differential equation, which violates the linearity condition necessary for superposition of solutions as outlined in Boyce and DiPrima's theorems.

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Homework Statement



Verify that y1(x) = 1 and y2(x) = x^.5 are solutions of the following y y'' + (y')^.5 = 0. Then show that c1 + c2 x^.5 is not in general a solution of this equation.

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The Attempt at a Solution



I was able to show that both y1 and y2 are solutions to the DE. I found the Wronskian to be 1/(2 sqrt(x)) which is not equal to zero, so I was under the impression that this would mean that the two solutions would form a fundamental set of solution. Does anyone see why c1 + c2 x^.5 isn't a solution?
 
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Your ODE isn't linear.
 
Does it matter if it's not linear in general? Boyce/Diprima's theorems don't seem to make note of whether or not the ODE must be linear for a set of fundamental solutions to be valid.
 
I'd have to see the theorem, but linearity is the property that tells you if y1 and y2 are solutions to an ODE then so is c1*y1+c2*y2. I think you need it.
 

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