Chain Rule

  • Thread starter oswald
  • Start date
  • #1
oswald
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Homework Statement


Finda dw/dt
w=3xy/x²-y²
x=t3
y=e2t

Homework Equations


w=(3t3e2t)/(t6-e4t)


The Attempt at a Solution


Well,is there anothe way to solve this, instead of dw/dt; like dw/dx * dw/dt + dw/dy * dy/dt ?

Homework Statement





Homework Equations





The Attempt at a Solution

 

Answers and Replies

  • #2
Dick
Science Advisor
Homework Helper
26,263
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Sure. You could just the chain rule as well. You should get the same answer both ways. Just substituting like you did looks to be a little easier.
 
  • #3
oswald
22
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Chain Rule Exponential and logarithmic

f(x) = ln [ e^ln(x+1) ]
f' = ?
 
  • #4
36,708
8,704
Simplify it a bit first to make your differentiation easier. What is ln(e^whatever)?
 
  • #5
oswald
22
0
f(x) = ln { e^[ln(x+1)] }

well, i have this answer, but i don't understand
ln [ e^ln(x+1) ] = ln(x+1)

f'(x) = 1/(e^ln(x+1)) * e^ln(x+1) * 1/(x+1) = 1/(x+1)
 
  • #6
36,708
8,704
The ln and exp functions are inverses of one another, so for any real number u, ln(eu) = u. This means that you can simplify your function before taking its derivative. Then, what you end up differentiating is much simpler.
 

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