MHB Continuity of the Inverse Function

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The discussion focuses on the continuity of inverse functions in calculus. It clarifies that for a function to have a continuous inverse, the original function must be one-to-one and continuous on its domain. The example provided, involving the functions y = -2/(x-5) and its inverse, illustrates confusion regarding their domains, which are not both R. The key takeaway is that if the original function is continuous and one-to-one, its inverse will also be continuous. Understanding these properties is essential for grasping the theorem on inverse functions.
bsmithysmith
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I just started Calculus 1, a summer quarter that's compressed and I'm having trouble understanding a theorem that state continuity of the inverse function. Within my textbook, it mentions "If f(x) is continuous on an interval I with range R, and if inverse f(x) exists, then the inverse f(x) is continuos with domain R".

Not understanding it too much, but from what I can derive from it is that when a function has an inverse, it follows the same rules of the function; if that makes sense.

Lets say:

$$y=\frac{-2}{x-5}$$
and the inverse
$$y=\frac{5x-2}{x}$$

Then they both are continuous with their domains R. Maybe I'm not getting it, or can't put it in words, but it's a little confusing to me. They are the same equations, although inverses, but follow the same properties of continuity.

I need simplification because I also don't understand what I'm talking about, myself.
 
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bsmithysmith said:
I just started Calculus 1, a summer quarter that's compressed and I'm having trouble understanding a theorem that state continuity of the inverse function. Within my textbook, it mentions "If f(x) is continuous on an interval I with range R, and if inverse f(x) exists, then the inverse f(x) is continuos with domain R".

Not understanding it too much, but from what I can derive from it is that when a function has an inverse, it follows the same rules of the function; if that makes sense.

Lets say:

$$y=\frac{-2}{x-5}$$
and the inverse
$$y=\frac{5x-2}{x}$$

Then they both are continuous with their domains R. Maybe I'm not getting it, or can't put it in words, but it's a little confusing to me. They are the same equations, although inverses, but follow the same properties of continuity.

I need simplification because I also don't understand what I'm talking about, myself.

Well first of all, it should be obvious that NEITHER of those functions has a domain of $\displaystyle \begin{align*} \mathbf{R} \end{align*}$.

Anyway, all that the theorem you're referring to is saying is that provided your original function is one-to-one on its domain (which is a requirement to have an inverse function), if your original function is continuous, so is the inverse function.
 
There are probably loads of proofs of this online, but I do not want to cheat. Here is my attempt: Convexity says that $$f(\lambda a + (1-\lambda)b) \leq \lambda f(a) + (1-\lambda) f(b)$$ $$f(b + \lambda(a-b)) \leq f(b) + \lambda (f(a) - f(b))$$ We know from the intermediate value theorem that there exists a ##c \in (b,a)## such that $$\frac{f(a) - f(b)}{a-b} = f'(c).$$ Hence $$f(b + \lambda(a-b)) \leq f(b) + \lambda (a - b) f'(c))$$ $$\frac{f(b + \lambda(a-b)) - f(b)}{\lambda(a-b)}...

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