My Math Forum > Math Derivatives

 Math General Math Forum - For general math related discussion and news

 January 24th, 2019, 02:48 AM #1 Member   Joined: Feb 2018 From: Iran Posts: 38 Thanks: 3 Derivatives The answer in my book is 5 but if we put 5 instead of x all of them are differentiable
 January 24th, 2019, 03:02 AM #2 Global Moderator   Joined: Dec 2006 Posts: 20,475 Thanks: 2039 $|x^2 - 4|$ isn't differentiable at Â±2 (two values of $x$), $\text{sgn}(x^3 + x)$ isn't differentiable at 0, etc.
 January 24th, 2019, 03:10 AM #3 Senior Member   Joined: May 2016 From: USA Posts: 1,310 Thanks: 551 You are misreading the question. It is not asking for the actual values of x where f(x) is not differentiable. It is asking how many such values there are. Thanks from idontknow
 January 24th, 2019, 04:59 AM #4 Senior Member   Joined: Sep 2016 From: USA Posts: 599 Thanks: 366 Math Focus: Dynamical systems, analytic function theory, numerics Unrelated comment: This is truly a terrible question. Whoever assigned it isn't paying attention. The only reasonable answer is 3, not 5. It only makes sense to talk about differentiability of a function on its domain. Functions don't "see" anything that isn't in their domain. Both of the following sentences make an equal amount of sense. 1. $f$ is not differentiable at $x = \frac{1}{\sqrt{2}}$. 2. $f$ is not differentiable at $x =$ 1998 Honda Accord. Thanks from topsquark Last edited by skipjack; January 24th, 2019 at 11:52 AM.
 January 24th, 2019, 01:28 PM #5 Global Moderator   Joined: May 2007 Posts: 6,730 Thanks: 689 $x^2-4=0$, 2 values. $x^3+x=0$, 1 real value. $2x^2-1=0$, 2 values. Total 5 (real) values. Thanks from idontknow
 January 24th, 2019, 02:06 PM #6 Senior Member   Joined: Dec 2015 From: iPhone Posts: 482 Thanks: 73 It is enough to know how to find the derivative , then the domain can be found easily .

 Tags derivatives

 Thread Tools Display Modes Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post John Travolski Calculus 9 September 6th, 2016 08:37 AM johngalt47 Calculus 2 November 23rd, 2013 11:44 AM r-soy Calculus 2 November 28th, 2010 05:52 PM r-soy Calculus 1 November 27th, 2010 08:58 PM r-soy Calculus 2 November 27th, 2010 08:26 AM

 Contact - Home - Forums - Cryptocurrency Forum - Top