July 29, 2014

Homework Help: Calc

Posted by Jamie on Tuesday, January 16, 2007 at 4:52pm.

a) y =ln(x-1) find dy/dx=?
b) y=3 ln x - ln (1/x) where x >0, dy/dx= ?

My teacher says the answers are a) (2x)/(x^2-1) and b) 4/x
I am not sure how you find the derivative when they involve ln. Could you please explain to me how to get these answers? I have a quiz on them soon so I just want to clearify how you would solve them. Thanks.

<<I am not sure how you find the derivative when they involve ln.>>

The derivative of ln x is 1/x. Use the "function of a function" rule when the log is of a function of x. For example:
y = ln (x-1)
Let u(x) = x-1
dy/dx = d (ln u)/du * du/dx = 1/u
= 1/(x-1)
You teacher is wrong on that one.

(2x)/(x^2-1)is the derivative of
ln (x^2 -1)
Perhaps you copied the problem wrong.

If y = 3 ln x - ln (1/x)
y = 3 ln x + ln x = 4 ln x
dy/dx = 4/x

Answer this Question

First Name:
School Subject:

Related Questions

Introduction to Educational Theory - We have to analyze this situation: A ...
Early Child Ed. - Please check these questions and my answers: 1.For children ...
Math - I Don't Know What Is This Subject Called In English But It's About ...
calc - f(x)=6(sin(x))^x, find f'(1). and f(x)=3x^ln(x), find f'(9). i tried ...
Algebra - I am having trouble with finding the 1st and 3rd quartiles of a set of...
IQ - What is IQ??? Like when a teacher says this says it in your IQ. One time ...
Sin/Cos - I'm having trouble with a concept. I don't understand how the answer ...
Early Child Ed. - Would you please check these questions and my answers? If my ...
basic Integration - I have three questions which I apparently have 'wrong' ...
calculus - Find the distance from (3,7,-5) to each of the following. a. the xy-...