# Question: When does the derivative not exist?

## How do you know if a derivative is undefined?

If there derivative can’t be found, or if it’s undefined, then the function isn’t differentiable there. So, for example, if the function has an infinitely steep slope at a particular point, and therefore a vertical tangent line there, then the derivative at that point is undefined.

## Where can you not take a derivative?

1, the derivative f′(a) exists precisely when the limit limx→af(x)−f(a)x−a lim x → a f ( x ) − f ( a ) x − a exists. That limit does not exist when the curve y=f(x) y = f ( x ) does not have a tangent line at x=a or when the curve does have a tangent line, but the tangent line has infinite slope.

## When can a function not be differentiable?

A function which jumps is not differentiable at the jump nor is one which has a cusp, like |x| has at x = 0. Generally the most common forms of non-differentiable behavior involve a function going to infinity at x, or having a jump or cusp at x.

## Why does the derivative not exist at a sharp point?

Each point in the derivative of a function represents the slope of the function at that point. In the case of a sharp point, the limit from the positive side differs from the limit from the negative side, so there is no limit. The derivative at that point does not exist.

## Can a derivative exist at a hole?

The derivative of a function at a given point is the slope of the tangent line at that point. So, if you can‘t draw a tangent line, there’s no derivative — that happens in cases 1 and 2 below. A removable discontinuity — that’s a fancy term for a hole — like the holes in functions r and s in the above figure.

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## Can derivatives be zero?

The derivative of a function, f(x) being zero at a point, p means that p is a stationary point. That is, not “moving” (rate of change is ). For example, f(x)=x2 has a minimum at x=, f(x)=−x2 has a maximum at x=, and f(x)=x3 has neither. You can see this by looking at the derivative to the left and right.

## Can a function be differentiable but not continuous?

When a function is differentiable it is also continuous. But a function can be continuous but not differentiable. For example the absolute value function is actually continuous (though not differentiable) at x=0.

## Do limits exist at corners?

The limit is what value the function approaches when x (independent variable) approaches a point. takes only positive values and approaches 0 (approaches from the right), we see that f(x) also approaches 0. itself is zero! exist at corner points.

## How do you know if a function is differentiable?

A piecewise function is differentiable at a point if both of the pieces have derivatives at that point, and the derivatives are equal at that point. In this case, Sal took the derivatives of each piece: first he took the derivative of x^2 at x=3 and saw that the derivative there is 6.

## How do you know if a graph is not differentiable?

A function is not differentiable at a if its graph has a vertical tangent line at a. The tangent line to the curve becomes steeper as x approaches a until it becomes a vertical line. Since the slope of a vertical line is undefined, the function is not differentiable in this case.

## What’s the derivative of E X?

Derivative Rules

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Common Functions Function Derivative
Exponential ex ex
ax ln(a) ax
Logarithms ln(x) 1/x
loga(x) 1 / (x ln(a))

## How do you know if a function is continuous?

Saying a function f is continuous when x=c is the same as saying that the function’s two-side limit at x=c exists and is equal to f(c).

## Are endpoints critical points?

A critical point is an interior point in the domain of a function at which f ‘ (x) = 0 or f ‘ does not exist. So the only possible candidates for the x-coordinate of an extreme point are the critical points and the endpoints.

## What does Second derivative tell?

The second derivative measures the instantaneous rate of change of the first derivative. The sign of the second derivative tells us whether the slope of the tangent line to f is increasing or decreasing. In other words, the second derivative tells us the rate of change of the rate of change of the original function.

## What does it mean when the second derivative does not exist?

A point x=c is an inflection point if the function is continuous at that point and the concavity of the graph changes at that point. And a list of possible inflection points will be those points where the second derivative is zero or doesn’t exist.