MHB 1.4.203 AP calculus practice question on Limits

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The discussion revolves around an AP Calculus practice question focused on finding the limit as x approaches π for the expression (cos x + sin x + 1) / (x² - π²). The solution involves recognizing the indeterminate form 0/0 and applying L'Hôpital's Rule, leading to the limit of -1/(2π). The correct answer is option (A) -1/(2π). Participants are encouraged to provide feedback on the solution for any typos or suggestions. Overall, the solution is confirmed to be accurate and well-presented.
karush
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I am posting some AP calculus practice questions on MeWe so thot I would pass them thru here first
The solution is mine...
any typos or suggestions...

$\textbf{Find the Limit of}$
$\displaystyle\lim_{x\to \pi} \dfrac{\cos{x}+\sin{x}+1}{x^2-\pi^2}$
(A) $-\dfrac{1}{2\pi}$
(B) $\dfrac{1}{\pi}$
(C) $1$
(D) DNE
$\textbf{Solution}$
By observation we have $\frac{0}{0}$ so apply L'Hopital's Rule
apply LH'R then plug in $\pi$ and simplify
$$\displaystyle\lim _{x\to \:\pi }
\left(\frac{\cos \left(x\right)-\sin \left(x\right)}{2x}\right)
=\dfrac{-1-0}{2\pi}=-\dfrac{1}{2\pi} \quad (A)$$
 
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karush said:
I am posting some AP calculus practice questions on MeWe so thot I would pass them thru here first
The solution is mine...
any typos or suggestions...

$\textbf{Find the Limit of}$
$\displaystyle\lim_{x\to \pi} \dfrac{\cos{x}+\sin{x}+1}{x^2-\pi^2}$
(A) $-\dfrac{1}{2\pi}$
(B) $\dfrac{1}{\pi}$
(C) $1$
(D) DNE
$\textbf{Solution}$
By observation we have $\frac{0}{0}$ so apply L'Hopital's Rule
apply LH'R then plug in $\pi$ and simplify
$$\displaystyle\lim _{x\to \:\pi }
\left(\frac{\cos \left(x\right)-\sin \left(x\right)}{2x}\right)
=\dfrac{-1-0}{2\pi}=-\dfrac{1}{2\pi} \quad (A)$$
Looks good to me.

-Dan
 
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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