Applications of Derivatives - AP Calculus BC

Let's examine the limit

first.

and

,

so by L'Hospital's Rule,

Since ,

Now, for each , ; therefore,

By the Squeeze Theorem,

and

Therefore, by L'Hospital's Rule, we can find by taking the derivatives of the expressions in both the numerator and the denominator:

Similarly,

So

But for any , so

and

Therefore, by L'Hospital's Rule, we can find by taking the derivatives of the expressions in both the numerator and the denominator:

Similarly,

so

We start at x = 0 and move to x=2, with a step size of 1. Essentially, we approximate the next step by using the formula:

.

So applying Euler's method, we evaluate using derivative:

And two step sizes, at x = 1 and x = 2.

And thus the evaluation of p at x = 2, using Euler's method, gives us p(2) = 2.

To calculate the limit, often times we can just plug in the limit value into the expression. However, in this case if we were to do that we get , which is undefined.

What we can do to fix this is use L'Hopital's rule, which says

.

So, L'Hopital's rule allows us to take the derivative of both the top and the bottom and still obtain the same limit.

.

Plug in to get an answer of .

Using Euler's method with means that we use two iterations to get the approximation. The general iterative formula is

where each is

is an approximation of , and , for this differential equation. So we have

So our approximation of is

Subbing in zero into will give you , so we can try to use L'hopital's Rule to solve.

First, let's find the derivative of the numerator.

is in the form , which has the derivative , so its derivative is .

is in the form , which has the derivative , so its derivative is .

The derivative of is so the derivative of the numerator is .

In the denominator, the derivative of is , and the derivative of is . Thus, the entire denominator's derivative is .

Now we take the

, which gives us .

L'Hopital's Rule is used to evaluate complicated limits. The rule has you take the derivative of both the numerator and denominator individually to simplify the function. In the given function we take the derivatives the first time and get

.

This still cannot be evaluated properly, so we will take the derivative of both the top and bottom individually again. This time we get

.

Now we have only one x, so we can evaluate when x is infinity. Plug in infinity for x and we get

and .

So we can simplify the function by remembering that any number divided by infinity gives you zero.

L'Hopital's Rule is used to evaluate complicated limits. The rule has you take the derivative of both the numerator and denominator individually to simplify the function. In the given function we take the derivatives the first time and get

.

Since the first set of derivatives eliminates an x term, we can plug in zero for the x term that remains. We do this because the limit approaches zero.

This gives us

.

L'Hopital's Rule is used to evaluate complicated limits. The rule has you take the derivative of both the numerator and denominator individually to simplify the function. In the given function we take the derivatives the first time and get

.

This still cannot be evaluated properly, so we will take the derivative of both the top and bottom individually again. This time we get

.

Now we have only one x, so we can evaluate when x is infinity. Plug in infinity for x and we get

.

If we plugged in directly, we would get an indeterminate value of .

We can use L'Hopital's rule to fix this. We take the derivate of the top and bottom and reevaluate the same limit.

.

We still can't evaluate the limit of the new expression, so we do it one more time.

When you try to solve the limit using normal methods, you find that the limit approaches zero in the numerator and denominator, resulting in an indeterminate form "0/0".

In order to evaluate the limit, we must use L'Hopital's Rule, which states that:

when an indeterminate form occurs when evaluting the limit.

Next, simply find f'(x) and g'(x) for this limit:

The derivatives were found using the following rules:

,

Next, using L'Hopital's Rule, evaluate the limit using f'(x) and g'(x):

Through direct substitution, we see that the limit becomes

which is in indeterminate form.

As such we can use l'Hospital's Rule, which states that if the limit

is in indeterminate form, then the limit is equivalent to

Taking the derivatives we use the power rule which states

Using the power rule the limit becomes

As such the limit exists and is

Through direct substitution, we see that the limit becomes

which is in indeterminate form.

As such we can use l'Hospital's Rule, which states that if the limit

is in indeterminate form, then the limit is equivalent to

Taking the derivatives we use the trigonometric rule which states

where is a constant.

Using l'Hospital's Rule we obtain

And through direct substitution we find

As such the limit exists and is

By substituting the value of , we will find that this will give us the indeterminate form . This means that we can use L'Hopital's rule to solve this problem.

L'Hopital states that we can take the limit of the fraction of the derivative of the numerator over the derivative of the denominator. L'Hopital's rule can be repeated as long as we have an indeterminate form after every substitution.

Take the derivative of the numerator.

Take the derivative of the numerator.

Rewrite the limit and use substitution.

The limit is .

Directly evaluating for yields the indeterminate form

we are able to apply L'Hospital's rule which states that if the limit is in indeterminate form when evaluated, then

As such the limit in the problem becomes

Evaluating for yields

As such

and thus

This important limit from elementary limit theory is usually proven using trigonometric arguments, but it can be shown using L'hopital's rule too.

When evaluating the limit using normal methods, we find that the indeterminate form results. When this occurs, we must use L'Hopital's Rule, which states that for .

Taking the derivative of the top and bottom functions and evaluating the limit, we get

The derivatives were found using the following rules:

, ,

When evaluating the limit using normal methods (substitution), we get the indeterminate form . When this (or ) occurs, we must use L'Hopital's Rule to evaluate the limit. The rule states that when an indeterminate form results from the limit,

Taking the derivatives in our limit, we get

The derivatives were found using the following rules:

, , ,