Derivative of Product of n Functions by Induction

In summary, the product rule states that when differentiating a product, the sum of the derivatives of the individual terms must be equal to the derivative of the product.
  • #1
ben.tien
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Homework Statement

: Let f1,...fn be n functions having derivatives f'1...f'n. Develop a rule for differentiating the product g = f1***fn and prove it by mathematical induction. Show that for those points x, where none of the function values f1(x),...fn(x) are zero, we have g'(x)/g(x) = (f'1(x)/f1(x))+...(f'n(x))/(fn(x))

Homework Equations


product rule: (f1*f2) = (f'1*f2 + f1*f'2)

The Attempt at a Solution

: So I used the associativity property to bunch up the n functions into n/2 functions : (f'1*f2 + f1*f'2)...(f'n-1*fn + fn-1*f1n) and that's where I got stuck.
 
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  • #2
ben.tien said:

Homework Statement

: Let f1,...fn be n functions having derivatives f'1...f'n. Develop a rule for differentiating the product g = f1***fn and prove it by mathematical induction. Show that for those points x, where none of the function values f1(x),...fn(x) are zero, we have g'(x)/g(x) = (f'1(x)/f1(x))+...(f'n(x))/(fn(x))



Homework Equations


product rule: (f1*f2) = (f'1*f2 + f1*f'2)


The Attempt at a Solution

: So I used the associativity property to bunch up the n functions into n/2 functions : (f'1*f2 + f1*f'2)...(f'n-1*fn + fn-1*f1n) and that's where I got stuck.
Show us what you did. For an induction proof, you need to establish a base case, and then assume that the statement is true when n = k. Then you need to show that when the statement for n = k is true, the statement for n = k + 1 must also be true.
 
  • #3
Okay. I've established that (f1*f2*f3)' = (f'1*f2 + f1*f'2)f3 + f1f2f'3 = f'1f2f3 + f1f'2f3+ f1f2f'3 and etc. for f1*...*fn. When n=k, (f1*...fk)' = f'1...fk + f1f'2...fk +...+ f1...f'k and for n=k+1 [f'1...fk*f(k+1)] +...+ [f1...f'k*f(k+1)] + [f1...fk*f'(k+1)]. However that seemed too easy and I'm sure this is right.
 
  • #4
Okay I see it now. Thanks.
 

1. What is a derivative proof by induction?

A derivative proof by induction is a mathematical technique used to prove that a certain property holds for all values of a variable in a given range. It involves using the fact that the derivative of a function at a particular point is equal to the limit of the difference quotient as the point approaches that value.

2. How is a derivative proof by induction different from a regular proof by induction?

In a regular proof by induction, the property being proved is based on a discrete set of values, while in a derivative proof by induction, the property is based on a continuous range of values. This means that instead of using discrete steps, the proof relies on the use of limits and derivatives.

3. What are the steps involved in a derivative proof by induction?

The steps involved in a derivative proof by induction are:

  • Prove the base case, which is the value of the property at the starting point of the range.
  • Assume that the property holds for a particular value, and prove that it also holds for the next value in the range.
  • Use the definition of the derivative to show that the property holds for the entire range.
  • Conclude that the property holds for all values in the given range.

4. What are the advantages of using a derivative proof by induction?

Some advantages of using a derivative proof by induction include:

  • It allows for the proof of properties that are based on continuous values, which cannot be proven using regular induction.
  • It is a more efficient and elegant method, as it uses the power of calculus to prove properties.
  • It can be applied to a wide range of mathematical concepts, such as limits, derivatives, and integrals.

5. Can a derivative proof by induction be used to prove any property?

No, a derivative proof by induction can only be used to prove properties that are based on continuous values and can be expressed using calculus. It cannot be used to prove properties that are based on discrete values or do not involve calculus.

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