Finding Roots of Derivatives on Casios

11192022, 05:03 AM
Post: #1




Finding Roots of Derivatives on Casios
Hi all. I put in the expression d/dx(3x^310x^2+15) x=x
Next, I opened SOLVE and put in an initial guess. After I press =, I get Syntax Error. So, I entered the same thing, except I set x=x. Nope. Syntax Error again. So, I tried writing it as 0=d/dx(3x^310x^2+15) and pressed SOLVE. Put in an initial guess. Nope. Syntax error. If there’s a way to find roots of derivatives on the 991, 115, and ClassWiz models, how do I do that? Thanks 

11192022, 11:26 AM
Post: #2




RE: Finding Roots of Derivatives on Casios
For 115/991: excerpt from UG
Important! If an equation contains input functions that include an open parenthesis (such as sin and log), do not omit the closing parenthesis. The following functions are not allowed inside of an equation: ∫, d/dx, Σ, Pol, Rec. https://support.casio.com/global/en/calc...SOLVE.html For 991EX (ClassWiz) d/dx(3x^310x^2+15) /x=A=0; solve for A, the 2nd equation sign next to the 0 is red on the keyboard (alpha+calc) press shift+calc (solve) scroll down to see A (not X) and enter value press enter to get the root x=2.2222222222 or 20/9 and x=0 

11192022, 09:42 PM
Post: #3




RE: Finding Roots of Derivatives on Casios
(11192022 11:26 AM)klesl Wrote: For 115/991: excerpt from UG Thanks! That works. 

11202022, 07:13 AM
Post: #4




RE: Finding Roots of Derivatives on Casios
Okay. Now I’ve got a first root.
How do I store this first root and repeat the process with a different estimate/guess and store that solution? I tried a STO A from the LR screen but it gets all messed up and I cannot see my equation in the history list. So, either I'm missing a step or my procedure is wonky. Please advise. Thanks. 

11202022, 05:35 PM
Post: #5




RE: Finding Roots of Derivatives on Casios
Well, you don't need to store the root because the root is stored automatically to memory A.
To find another root, just use solver again: When you see the root and LR on the screen, press the right arrow and change initial value from A to B and start solver. Now you have 2 roots stored in A and B 

11202022, 11:09 PM
Post: #6




RE: Finding Roots of Derivatives on Casios
(11202022 05:35 PM)klesl Wrote: Well, you don't need to store the root because the root is stored automatically to memory A. Thanks! I definitely know what you mean. 

11202022, 11:21 PM
(This post was last modified: 11202022 11:30 PM by Matt Agajanian.)
Post: #7




RE: Finding Roots of Derivatives on Casios
On another tangent (pun intended).
Is there such a thing as finding roots of derivatives by deflation? For example: With a as the first root of f’(x) is it legitimate to apply the deflation formula of f’(x)/(xa) to find the second zero, thus the second extremum? Or is there another formula instead? 

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