### All AP Calculus AB Resources

## Example Questions

### Example Question #1 : Geometric Understanding Of Graphs Of Continuous Functions

is differentiable for which of the following values of ?

**Possible Answers:**

**Correct answer:**

is not differentiable at and because the values are discontinuities. is not differentiable at because that point is a corner, indicating that the one-side limits at are different. is differentiable:the one side limits are the same and the point is continuous.

### Example Question #2 : Geometric Understanding Of Graphs Of Continuous Functions

Consider the graph of above. What can we say about when ?

**Possible Answers:**

has a horizontal tangent at .

Two or more of these are correct.

None of these are correct.

has a removable discontinuity at .

is discontinuous at because there is a sharp turn at .

**Correct answer:**

has a horizontal tangent at .

Note that , indicating that there is a horizontal tangent on at . More specifically, the derivative is the slope of the tangent line. If the slope of the tangent line is 0, then the tangent is horizontal.

The other two are incorrect because sharp turns only apply when we want to take the derivative of something. The derivative of a function at a sharp turn is undefined, meaning the graph of the derivative will be discontinuous at the sharp turn. (To see why, ask yourself if the slope at is positive 1 or negative 1?) On the other hand, integration is less picky than differentiation: We do not need a smooth function to take an integral.

In this case, to get from to , we took an integral, so it didn't matter that there was a sharp turn at the specified point. Thus, neither function had any discontinuities.

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