 # Question: What Does 2nd Derivative Tell You?

## When can you not use the second derivative test?

If f'(x) doesn’t exist then f”(x) will also not exist, so the second derivative test is impossible to carry out..

## Why does the second derivative test fail?

If f ′(c) = 0 and f ″(c) < 0, then f has a local maximum at c. Else, the test fails (if f ′(c) doesn't exist, or f ″(c) = 0, or f ″(c) doesn't exist). Note: Even though it is often easier to use than the first derivative test, the second derivative test can fail at some points, as noted above.

## Why does the second derivative determine concavity?

If the second derivative of a function f(x) is defined on an interval (a,b) and f ”(x) > 0 on this interval, then the derivative of the derivative is positive. Thus the derivative is increasing! In other words, the graph of f is concave up. Similarly, if f ”(x) < 0 on (a,b), then the graph is concave down.

## How do you do the second derivative test?

Set f ‘ (x) = 0, and solve for x. Plug your solution(s) from step 2 into f ‘ ‘ (x) and use the rules set forth in the second derivative test to determine if there is a maximum or minimum point at these values. Plug the same values (from step 2) back into f(x) to find the actual value of the relative maxima or minima.

## How do you interpret the second derivative graph?

This is read aloud as “the second derivative of f. If f″(x) is positive on an interval, the graph of y = f(x) is concave up on that interval. We can say that f is increasing (or decreasing) at an increasing rate. If f″(x) is negative on an interval, the graph of y = f(x) is concave down on that interval.

## What is the difference between first and second derivative?

The first derivatives are used to find critical points while the second derivative is used to find possible points of inflection. By itself, a first derivative equal to 0 at a point does not tell you whether that point is actually an extrema.

## What does it mean when the second derivative test fails?

If f (x0) = 0, the test fails and one has to investigate further, by taking more derivatives, or getting more information about the graph. Besides being a maximum or minimum, such a point could also be a horizontal point of inflection.

## What is the second derivative rule?

If the second derivative is positive over an interval, indicating that the change of the slope of the tangent line is increasing, the graph is concave up over that interval. … CONCAVITY TEST: If f ”(x) < 0 over an interval, then the graph of f is concave upward over this interval.

## What happens when the second derivative is 0?

The second derivative is zero (f (x) = 0): When the second derivative is zero, it corresponds to a possible inflection point. If the second derivative changes sign around the zero (from positive to negative, or negative to positive), then the point is an inflection point.

## What does a positive second derivative mean?

As stated above, if the second derivative is positive, it implies that the derivative, or slope is increasing, while if it is negative, implies that the slope is decreasing. As a graphical example, consider the graph, y=(x)(x−2)(x−3) which looks like this.

## What does the first derivative tell you?

The first derivative of a function is an expression which tells us the slope of a tangent line to the curve at any instant. Because of this definition, the first derivative of a function tells us much about the function. If is positive, then must be increasing. If is negative, then must be decreasing.

## What is the second derivative test used for?

The second derivative may be used to determine local extrema of a function under certain conditions. If a function has a critical point for which f′(x) = 0 and the second derivative is positive at this point, then f has a local minimum here.