# AP Calculus AB : Geometric understanding of graphs of continuous functions

## Example Questions

### Example Question #111 : Ap Calculus Ab  is differentiable for which of the following values of      Explanation: 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 #1 : Continunity As A Property Of Functions  Consider the graph of above. What can we say about when ? has a horizontal tangent at . is discontinuous at because there is a sharp turn at .

None of these are correct. has a removable discontinuity at .

Two or more of these are correct. has a horizontal tangent at .

Explanation:

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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