Logarithmic Differentiation of (x+5)(x+9): Where Did I Go Wrong?

In summary, the student attempted to find the derivative of the given function using logarithmic differentiation. After some calculations, they realized that their process was correct and they were able to find the correct derivative, which is 2x+14.
  • #1
vysero
134
0

Homework Statement



Find the derivative using logarithmic differentiation:
y=(x+5)(x+9)

The Attempt at a Solution



lny=ln(x^2+14x+45)
lny=(2x+14)/(x^2+14x+45)
y'=(x^2+14x+45)((2x+14)/(x^2+14x+45))However, I know the derivative of the function is actually 2x+14. So I am wondering what is wrong with my process?

UPDATE: Wow it only took typing my problem into this forum and making the post before I realized that I did do it right! You guys are good! lol sorry for wasting any ones time.
 
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  • #2
vysero said:

Homework Statement



Find the derivative using logarithmic differentiation:
y=(x+5)(x+9)

The Attempt at a Solution



lny=ln(x^2+14x+45)
lny=(2x+14)/(x^2+14x+45)
y'=(x^2+14x+45)((2x+14)/(x^2+14x+45))However, I know the derivative of the function is actually 2x+14. So I am wondering what is wrong with my process?

UPDATE: Wow it only took typing my problem into this forum and making the post before I realized that I did do it right! You guys are good! lol sorry for wasting any ones time.

Why wouldn't you just say :

lny=ln((x+5)(x+9))
ln y = ln(x+5) + ln(x+9)

Now...

y'/y = Take the derivative here

Would've been muchhhh easier.
 

FAQ: Logarithmic Differentiation of (x+5)(x+9): Where Did I Go Wrong?

What is logarithmic differentiation?

Logarithmic differentiation is a technique used to differentiate functions that involve both exponentials and logarithms. It involves taking the natural logarithm of both sides of the function and then using properties of logarithms to simplify the differentiation process.

Why is logarithmic differentiation useful?

Logarithmic differentiation is useful because it allows us to differentiate complicated functions that would be difficult to differentiate using traditional methods. It also allows us to easily differentiate functions with variables in both the base and exponent.

What are the steps involved in logarithmic differentiation?

The steps involved in logarithmic differentiation are as follows:

  • Take the natural logarithm of both sides of the function
  • Use properties of logarithms to simplify the function
  • Apply the power rule and chain rule to differentiate the function
  • Solve for the original function by exponentiating both sides

What types of functions can be differentiated using logarithmic differentiation?

Logarithmic differentiation can be used to differentiate functions that involve both exponentials and logarithms, such as functions in the form of y = a^x or y = log(x).

When should logarithmic differentiation be used?

Logarithmic differentiation should be used when traditional methods of differentiation become difficult or impossible due to the complexity of the function. It can also be used when the function involves both logarithms and exponentials.

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