# Maclaurin series

1. Apr 8, 2014

### delsoo

1. The problem statement, all variables and given/known data

for this question, i found that my coefficient of x^4 is wrong... after applying the maclaurin series formula, i would get the coefficient of X^4 is -5/96.... but the exact ans is -1/96... can anyone check which part is wrong?

2. Relevant equations

3. The attempt at a solution

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2. Apr 8, 2014

### Dick

For one thing y''(0)=(-1/2) not (+1/2). Can you check how you got that? I think you made an algebra mistake. Then can you spell out how you got y'''(0) and y''''(0) a little more clearly?

Last edited: Apr 8, 2014
3. Apr 9, 2014

### delsoo

this is actually the question from my book(gt it from my senior), do u mean the proving part, the third term is -1/2 y^2 ?? for y'''(0) and y''''(0) , i differentiate the equation y(d2y/dx2) + (dy/dx)^2 + 1/2y^2 a few times to get y''' and y'''' .... refer to the photo attached...

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4. Apr 9, 2014

### Dick

The photo you attached seems to be from a different problem and what you have in the original statement is pretty hard to read. I think if you do it again more carefully you should get the correct answer.

5. Apr 12, 2014

### delsoo

can you check my working again? i checked it many times but i just cant dont know where's my mistake

6. Apr 12, 2014

### Dick

I told you a long time ago. y''(0) should be -1/2, not +1/2. Didn't you check that?