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markmil2002
Average Member

USA
11 Posts

 Posted - 09/17/2007 :  19:19:19 I'm trying to find the derivitive of f(x) = (x + 1)/(ln x) After doing some math I got -2x/x but I don't think that is correct.

sahsjing

USA
2399 Posts

 Posted - 09/17/2007 :  20:27:52 You should have 1/(lnx) as a factor. Try it again?

Subhotosh Khan

USA
9117 Posts

 Posted - 09/18/2007 :  09:26:27 quote:Originally posted by markmil2002I'm trying to find the derivitive of f(x) = (x + 1)/(ln x) After doing some math I got -2x/x but I don't think that is correct.f(x) = u(x)/v(x)df/dx = (u'*v - v'*u)/v2.................(1)In your case:u(x) = x2 + 1 .................... u' = 2xv(x) = ln(x) ................................ v' = 1/xUsing these in (1)df/dx = [(2x) * ln(x) - (x2 + 1) * (1/x)]/{ln(x)}2Now simplify and continue...

markmil2002
Average Member

USA
11 Posts

 Posted - 09/18/2007 :  22:12:33 I've made it that far, but I dont see how to simplify. Obviously e will probably be involved to cancel ln, but I cant figure out how to apply it.quote:Originally posted by Subhotosh Khanquote:Originally posted by markmil2002I'm trying to find the derivitive of f(x) = (x + 1)/(ln x) After doing some math I got -2x/x but I don't think that is correct.f(x) = u(x)/v(x)df/dx = (u'*v - v'*u)/v2.................(1)In your case:u(x) = x2 + 1 .................... u' = 2xv(x) = ln(x) ................................ v' = 1/xUsing these in (1)df/dx = [(2x) * ln(x) - (x2 + 1) * (1/x)]/{ln(x)}2Now simplify and continue...
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