In order to find the critical points, we need to find  using the power rule .

Now we set , and solve for .

Thus  is a critical point.

To find the critical point(s) of a function , take its derivative , set it equal to , and solve for .

Given , use the power rule

 to find the derivative. Thus the derivative is, .

Since :

The critical point  is . 

In order to find the critical points, we must find  using the power rule .

.

Now we set .

Now we use the quadratic equation in order to solve for .

Remember that the quadratic equation is as follows.

,

where a,b,c correspond to the coefficients in the equation 

.

In this case, a=9, b=-40, c=4.

Then are critical points are:

In order to find the critical points, we first need to find  using the power rule ..

Now we set .

Thus the critical points are at

, and

.

To find critical points the derivative of the function must be found. 

Critical points occur where the derivative equals zero. 

To find the point where the graph of  is not changing, we must set the first derivative equal to zero and solve for .

To evaluate this derivate, we need the following formulae:

Now, setting the derivate equal to  to find where the graph is not changing:

Now, to find the corresponding  value, we plug this  value back into :

Therefore, the point where  is not changing is 

To evaluate this limit, we must use L'Hopital's Rule:

If  , take the derivative of both  and  and then plug in  to obtain 

We will also need the power rule, the derivative of the trigonometric function sine, and the chain rule.

Since when we plug in  in the numerator and denominator, we obtain a result of  , we can use L'Hopitals rule.

To take the derivative of the numerator we need the chain rule, the derivative of the trigonometric function sine, and the power rule.

Applying the chain rule to the numerator with  and , we see that:

 and .

Now plugging these into the chain rule, we obtain:

Now, to find the derivative of the denominator, we need the power rule again:

Now that we have found the derivative of the numerator and denominator, we can apply L'Hopital's Rule:

To evaluate this limit, all we need to do is factor the numerator and then cancel out the factor that is in common using the following formula:

With a simple algebra trick, we will be able to easily plug in  for :

To solve this problem, we need the chain rule,  the derivative of the trigonometric function cosine, and the power rule.

First let's apply the chain rule, which states:

In this problem,  and .

To find  , we need the power rule which states:

To find , we need the derivative of cosine which states:

Plugging these equations into the chain rule we obtain:

To find all points where the tangent line is horizontal, we must first take the derivative of the function and then set it equal to zero:

Setting this equal to zero, we obtain:

Therefore, either    or  

Recall that from the unit circle, cosine equals zero at   and sine equals zero at .

So, at every multiple of , either  or .  

Therefore,   because at each multiple of   , either   or 

To begin, we need L'Hopital's Rule for this problem which states that if you get  when you plug in the value into your function when evalutating the limit, you should take the derivative of both the numerator and the denominator and then try plugging in your value again. 

Since this is the case, we will take the derivative of the numerator and denominator.

To take the derivative of the numerator, we need the differentiation formulas for the trigonometric functions cosine and sine.

So, the derivative of the numerator is 

To find the derivative of the denominator, we again need the differentiation formula for cosine, as well as the chain rule.

In this problem,  and 

So, plugging these into the chain rule, we obtain:

Now let's put these expressions back into the numerator and denominator and again try to plug in our limit value: