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An Inverse Evaluation (Posted on 2006-05-25) Difficulty: 4 of 5
We know that f'(x) and f"(x) respectively denote the first derivative and second derivative of a given function f(x) with respect to x.
If P is the inverse function of S, and P'(x)=ex2; then:
2*S(x)*S'(x) + eS(x)2*S"(x) = ?

See The Solution Submitted by K Sengupta    
Rating: 4.0000 (2 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution re: Maybe the way? yes it is! | Comment 3 of 6 |
(In reply to Maybe the way? by e.g.)

By definition, for each real x:  P(S(x)) = x

Differentiate, using the Chain rule: P′(S(x))S′(x) = 1

Therefore:     exp (S(x)^2) * S′(x) = 1  .......... Eq (1)

Differentiate, using the Chain and Product rules:
     S′′(x) * exp (S(x)^2) +  S′(x) * exp (S(x)^2) * 2*S(x) * S′(x) = 0

Subsitute from Eq (1):     S′′(x) * exp (S(x)^2) + 2*S(x)S′(x) = 0

So the required answer is Zero.

Edited on February 19, 2015, 10:11 am
  Posted by JayDeeKay on 2006-05-30 16:18:56

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