Determining if a function has a cusp, vertical tangent, corner or none at a point

In summary, the conversation discusses the function y=x^3 + (x-3)^(1/3) and whether it has a vertical tangent, cusp, corner or none at x=3. The attempt at a solution involves taking the derivative, which is 3x^2 + 1 / 3x^(2/3). After replacing 3, it results in 27 + 1 / 0, suggesting a vertical line. However, the concavity on each side of x=3 must be considered to determine if it is a vertical tangent or cusp.
  • #1
crazco
15
0

Homework Statement




At x=3 does the function y=x^3 + (x-3)^(1/3) have a vertical tangent, cusp, corner or none?


The Attempt at a Solution



I took the derivative

y'=3x^2 + 1 / 3x^(2/3) then i replaced 3 in which gave 27 + 1 / 0

I don't understand how to come to the correct conclusion following this step.

Vertical tangent comes to mind since 1 / 0 is a vertical line, but I don't know how to prove it using limits.
 
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  • #2
You mean y'=3x^2 + 1 / 3(x-3)^(2/3), right? If you approach x=3 from below then y' goes to +infinity. I you approach it from above it also goes to +infinity. y is also continuous at x=3. Looks like a vertical tangent to me.
 
  • #3
crazco said:

Homework Statement




At x=3 does the function y=x^3 + (x-3)^(1/3) have a vertical tangent, cusp, corner or none?


The Attempt at a Solution



I took the derivative

y'=3x^2 + 1 / 3x^(2/3)

Is that really what you got?? It's either a typo or a mis-calculation.

then i replaced 3 in which gave 27 + 1 / 0

I don't understand how to come to the correct conclusion following this step.

Vertical tangent comes to mind since 1 / 0 is a vertical line, but I don't know how to prove it using limits.

If you have a positive infinite limit from both the left right that suggests a vertical line alright. You can tell whether it is vertical tangent line or cusp by looking at concavity on each side of x = 3.
 

What is a cusp in a function?

A cusp in a function occurs at a point where the function has a sharp turn and the derivative is undefined. This results in a point where the graph of the function has a "pointy" appearance.

How can I determine if a function has a cusp at a point?

To determine if a function has a cusp at a point, you can look at the behavior of the function and its derivative at that point. If the function has a sharp turn and the derivative is undefined at that point, then it has a cusp.

What is a vertical tangent in a function?

A vertical tangent in a function occurs at a point where the slope of the function is infinite, resulting in a vertical line. This usually happens at a point where the derivative is zero.

How can I determine if a function has a vertical tangent at a point?

To determine if a function has a vertical tangent at a point, you can look at the slope of the function and its derivative at that point. If the slope is infinite and the derivative is zero, then it has a vertical tangent.

What is a corner in a function?

A corner in a function occurs at a point where the function has a sharp turn and the derivative is defined. This results in a point where the graph of the function has an abrupt change in direction.

How can I determine if a function has a corner at a point?

To determine if a function has a corner at a point, you can look at the behavior of the function and its derivative at that point. If the function has a sharp turn and the derivative is defined at that point, then it has a corner.

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