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# Find and prove a formula for the derivative of a product of n differentiable functions

Let

be the product of functions with derivatives . Find a formula for the derivative of , and prove that it is correct by mathematical induction.

Furthermore, show that

for those at which for any .

Claim: If , then

Proof. For the case , from the usual product rule we have

Thus, our claimed formula holds in this case. Assume then that it is true for some integer . Then, if we have,

Therefore, if the formula holds for then it also holds for ; thus, it holds for all positive integers

Next, we prove the formula for the quotient, .

Proof. Let be defined as above, and let be a point at which for any . Then,

### One comment

1. Well I didn’t arrive to the same formula. I’ve arrived into a recursive formula which is:

$\\G_n(x) = G^I_{n-1}(x).F_n(x) + G_{n-1}(x).F^I_n(x)$

And can also be proved by induction