What Happens at the Cusp on the Original Graph When Viewing the Derivative?

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SUMMARY

The discussion centers on the behavior of derivatives at cusps in original graphs. When the original function, f, has a cusp, the derivative f' is undefined at that point, leading to an asymptote. Conversely, if the derivative graph f' exhibits a cusp, it indicates that the second derivative does not exist. The example of y = |x| illustrates this concept, where f'(x) = |x| leads to f(x) = (1/2)x² for x ≥ 0 and -(1/2)x² for x < 0, demonstrating the cusp's impact on the original graph.

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Students and professionals in mathematics, particularly those studying calculus, graph theory, and analytical geometry, will benefit from this discussion.

sarahr
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If the original graph, f, has a cusp, obviously the derivative is not defined at the x-value of the cusp (resulting in an asymptote).

but, what if you are viewing a graph of the derivative, f ', and it has a cusp.. what is going on at the x-value of the cusp on the original graph, f ?
 
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If the derivative graph has a cusp, that means that the second derivative does not exist. Think about y= |x| which does not have a derivative at x= 0. If we let f '(x)= |x| = (x if x>= 0 and -x if x< 0) and integrate we get
f(x)= ((1/2)x^2 if x>=0 and -(1/2)x^2 if x< 0). What does its graph look like around x= 0?
 
perfect example! thankss
 

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