All AP Calculus AB Resources
Example Questions
Example Question #72 : Derivative As A Function
At the point , is the function increasing or decreasing, concave or convex?
Increasing, concave
Increasing, convex
Decreasing, convex
The function is undefined at that point
Decreasing, concave
Decreasing, convex
First, let's find out if the graph is increasing or decreasing. For that, we need the first derivative.
To find the first derivative, we can use the power rule. We lower the exponent on all the variables by one and multiply by the original variable.
We're going to treat as since anything to the zero power is one.
Notice that since anything times zero is zero.
Plug in our given point for . If the result is positive, the function is increasing. If the result is negative, the function is decreasing.
Our result is negative, therefore the function is decreasing.
To find the concavity, look at the second derivative. If the function is positive at our given point, it is concave. If the function is negative, it is convex.
To find the second derivative we repeat the process, but using as our expression.
As you can see, our second derivative is a constant. It doesn't matter what point we plug in for ; our output will always be negative. Therefore our graph will always be convex.
Combine our two pieces of information to see that at the given point, the graph is decreasing and convex.
Example Question #3 : Finding Regions Of Concavity And Convexity
When , what is the concavity of the graph of ?
Increasing, concave
Decreasing, concave
Decreasing, convex
There is insufficient data to solve.
Increasing, convex
Increasing, convex
To find the concavity, we need to look at the first and second derivatives at the given point.
To take the first derivative of this equation, use the power rule. The power rule says that we lower the exponent of each variable by one and multiply that number by the original exponent:
Simplify:
Remember that anything to the zero power is equal to one.
The first derivative tells us if the function is increasing or decreasing. Plug in the given point, , to see if the result is positive (i.e. increasing) or negative (i.e. decreasing).
Therefore the function is increasing.
To find out if the function is convex, we need to look at the second derivative evaluated at the same point, , and check if it is positive or negative.
We're going to treat as since anything to the zero power is equal to one.
Notice that since anything times zero is zero.
Plug in our given value:
Since the second derivative is positive, the function is convex.
Therefore, we are looking at a graph that is both increasing and convex at our given point.
Example Question #2 : Finding Regions Of Concavity And Convexity
At the point , is increasing or decreasing, and is it concave or convex?
Increasing, convex
Decreasing, concave
Increasing, concave
The graph is undefined at point
Decreasing, convex
Decreasing, convex
To find out if the function is increasing or decreasing, we need to look at the first derivative.
To find the first derivative, we can use the power rule. We lower the exponent on all the variables by one and multiply by the original variable.
Anything to the zero power is one.
Now we plug in our given value and find out if the result is positive or negative. If it is positive, the function is increasing. If it is negative, the function is decreasing.
Therefore, the function is decreasing.
To find out if it is concave or convex, look at the second derivative. If the result is positive, it is convex. If it is negative, then it is concave.
To find the second derivative, we repeat the process using as our expression.
We're going to treat as .
Notice that since anything times zero is zero.
As stated before, anything to the zero power is one.
Since we get a positive constant, it doesn't matter where we look on the graph, as our second derivative will always be positive. That means that this graph is going to be convex at our given point.
Therefore, the function is decreasing and convex at our given point.
Example Question #12 : Calculus I — Derivatives
Define .
Give the interval(s) on which is decreasing.
is decreasing on those intervals at which .
We need to find the values of for which . To that end, we first solve the equation:
These are the boundary points, so the intervals we need to check are:
, , and
We check each interval by substituting an arbitrary value from each for .
Choose
increases on this interval.
Choose
decreases on this interval.
Choose
increases on this interval.
The answer is that decreases on .
Example Question #13 : Calculus I — Derivatives
Define .
Give the interval(s) on which is increasing.
is increasing on those intervals at which .
We need to find the values of for which . To that end, we first solve the equation:
These are the boundary points, so the intervals we need to check are:
, , and
We check each interval by substituting an arbitrary value from each for .
Choose
increases on this interval.
Choose
decreases on this interval.
Choose
increases on this interval.
The answer is that increases on
Example Question #3 : Derivatives
At what point does shift from increasing to decreasing?
It does not shift from increasing to decreasing
To find out where the graph shifts from increasing to decreasing, we need to look at the first derivative.
To find the first derivative, we can use the power rule. We lower the exponent on all the variables by one and multiply by the original variable.
We're going to treat as since anything to the zero power is one.
Notice that since anything times zero is zero.
If we were to graph , would the y-value change from positive to negative? Yes. Plug in zero for y and solve for x.
Example Question #1 : Derivatives
At what value of does shift from decreasing to increasing?
It does not shift from decreasing to increasing
To find out when the function shifts from decreasing to increasing, we look at the first derivative.
To find the first derivative, we can use the power rule. We lower the exponent on all the variables by one and multiply by the original variable.
Anything to the zero power is one.
From here, we want to know if there is a point at which graph changes from negative to positive. Plug in zero for y and solve for x.
This is the point where the graph shifts from decreasing to increasing.
Example Question #1 : Understanding L'hospital's Rule
Evaluate the following limit:
When approaches 0 both and will approach . Therefore, L’Hopital’s Rule can be applied here. Take the derivatives of the numerator and denominator and try the limit again:
Example Question #2 : Derivative Interpreted As An Instantaneous Rate Of Change
Find the instantaneous rate of change for the function,
at the point .
Find the instantaneous rate of change for the function,
at the point .
1) First compute the derivative of the function, since this will give us the instantaneous rate of change of the function as a function of .
2) Now evaluate the derivative at the value ,
Therefore, is the instantaneous rate of change of the function
at the point .
Example Question #3 : Derivative Interpreted As An Instantaneous Rate Of Change
A particle is traveling in a straight line along the x-axis with position function . What is the instantaneous rate of change in the particle's position at time seconds?
To find the instantaneous rate of change of the particle at time , we have to find the derivative of and plug into it.
.
And
.
Hence the instantaneous rate of change in position (or just 'velocity') of the particle at is . (At that very instant, the particle is not moving.)
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