Can someone tell me where i'm going wrong on this f"(x)

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lblue54

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Nov 8, 2008
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I have been on this problem for almost an hour and i can't find where i'm messing up...i know its gotta be something simple but i'm drawing a blank...i'm going through my chapter and working all of the problems...this and another one i'm having problems with, but i figure i'm making the same mistake on both

the problem is g(s) = s/(1+s)^2
i get...

g'(s)= 1-s^2/(1+s^2)^2

here's my work for g"(s)
G"(s)= (x-1)^2(12x^3-12x^2) - (3x^4-4x^3)(2)(x-1) / (x-1)^4
=(-2s)(1+s^2)[1+s^2-(1-s^2)(-1)/(1+s^2)^3
=(-2)(1+s^2+-s^2)/(1+s^2)^3
=(-2)(2)/(1+s^2)^3
=-4s/(1+s^2)^3

if u don''t mind can u show ur work for g"(s) so i can see my mistake, thanks a bunch!
 
lblue54 said:
I have been on this problem for almost an hour and i can't find where i'm messing up...i know its gotta be something simple but i'm drawing a blank...i'm going through my chapter and working all of the problems...this and another one i'm having problems with, but i figure i'm making the same mistake on both

the problem is g(s) = s/(1+s)^2

using chain rule

g'(s) = [(1+s)^2 - s*2*(1+s)]/(1+s)^4 = (1-s)/(1+s)^3

i get...

g'(s)= 1-s^2/(1+s^2)^2

here's my work for g"(s)
G"(s)= (x-1)^2(12x^3-12x^2) - (3x^4-4x^3)(2)(x-1) / (x-1)^4
=(-2s)(1+s^2)[1+s^2-(1-s^2)(-1)/(1+s^2)^3
=(-2)(1+s^2+-s^2)/(1+s^2)^3
=(-2)(2)/(1+s^2)^3
=-4s/(1+s^2)^3

if u don''t mind can u show ur work for g"(s) so i can see my mistake, thanks a bunch!
Click to expand...
 
g= s/[1+s]^2
g ' = [1+s]^2-s2[1+s] all over [1+s]^4
factor out [1+s] and cancel with term in the denominator
g '= [1+s-2s] all over [1+s]^3
g ' = [1-s] /[1+s]^3

g '' = [1+s]^3[-1] -[1-s]3[1+s]^2 all over [1+s]^6
factor out [1+s]^2 and cancel with term in denominator
g ' ' =[-1-s-3+3s] all over [1+s]^4
g ' ' = [2s-4] / [1+s]^4
g ' ' = 2[s-2]/[1+s]^4

Arthur
 


"Spoon feeding, in the long run, teaches us nothing but the shape of the spoon." ~ E. M. Forster

 
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