Hello, mohamedsafy!

It took me a few tries, but I got it . . .

First, we find the derivatives . . ..[1]

prove that: .

.[2]

. . which simplifies to: . .[3]

Then: .. . . . Substitute [1], [2] and [3]

. .

. .

. .There!

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- Nov 26th 2008, 04:04 AM #1

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- Nov 26th 2008, 05:51 AM #2

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- Nov 26th 2008, 06:01 AM #3

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## oh thxxxxx

thank u now i knew where was my error

thankx for all people in this forum u r really helping me too much to pass my exam tommorow i really apreciae it