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do you have a idea about it?can you help me
http://img17.imageshack.us/img17/1156/18176658.png
You're looking for a particular function, which, when added or subtracted with scalar multiples of its derivatives, will end up as 0. This means that the particular function and its derivatives need to be of the same "family". The exponential function is an obvious choice, because the exponential function is its own derivative (i.e. the derivatives will be in the same family).