(12-31-2019 06:53 PM)Kaliuzhkin Wrote: (11-21-2019 12:12 AM)Giuseppe Donnini Wrote: ... But there was much criticism about the contents [of the two-volume manual], people were not happy with the way new concepts, like RPL, were introduced, especially if they had skipped the HP-28C/S and came directly from the HP-41. The index was unsatisfactory to such a degree that Jake Schwartz decided to compile an improved one on his own: https://www.hpcalc.org/details/3562. Important information was also lacking, e.g. the special use of the "@" character, allowing comments to be inserted within programs, wasn't mentioned anywhere.
HP eventually reacted to the criticism, and the result was the one-volume version of the HP-48SX manual, for which they (slightly) rewrote almost every single chapter, greatly improved the index, and added new information here and there....
I've been working my way through the two-volume Owner's Manual and came across a serious and gross error. The error is so severe that it makes me wonder if anybody who wrote this manual passed high school Mathematics.
The error is in Volume I, Chapter 22, Summary Examples, pages 410 - 412. Example 1 is to "Solve for x in the equation: (3/(2*x-1)) + 4 = (6*x/(2*x-1)". The text goes on to show how the equation can be manipulated using Rules Transformations in Equation Writer so that it becomes an equation (3+2*X=4) in which x appears only once. This equation is moved to the stack and ISOL is used to solve for x: x = 0.5.
The problem is that this value of x is not in the domain of the original equation! The equation is undefined at this value of x since the denominators are zero. The technique shown in the Owner's Manual is improper. Neither the HP Solve Equation nor Plotting can be used to solve the equation.
In high school mathematics, you learn that the first thing you must do when studying an equation is to determine its domain. The domain for (3/(2*x-1)) + 4 = (6*x/(2*x-1) is x ≠ 0.5. For x = 0.5, the denominators are zero. You can't divide by zero. Therefore, it is improper to move the denominators 2*x-1 to the numerator, as in step 6. The technique shown in the book is wrong!
Maybe this example could be patched up by using the calculus concepts of limit but, why over-complicate things? It would be better to use another example, an example which doesn't divide by zero.
Fortunately, the single volume Owner's Manual does not include this error.
By the way, the concept of "domain" might seem obscure, but here is an example where domain is critical to the problem.
There are several errors, some documented here:
https://www.hpcalc.org/hp48/docs/misc/sxmanualerr.txt
One of my long term projects was to OCR the scans and apply all the fixes.
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