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Topic: Microsoft Algebra Question (Read 10872 times) |
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farsed
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Re: Microsoft Algebra Question
« Reply #25 on: Mar 2nd, 2005, 12:23am » |
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the solution is this -x^2 == x^2 == -x * -x and thats why the left part is x^2 - x^2 = 0
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Icarus
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Re: Microsoft Algebra Question
« Reply #26 on: Mar 2nd, 2005, 4:24pm » |
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Not by standard conventions of mathematics: exponentiation has precedence over - (both unary and binary):
-x2 = -(x2) = -(x * x), AND NOT (-x)2 = (-x * -x).
Unfortunately, certain languages, including VBasic which Excel uses, have chosen to give unary - precedence over exponentiation, contrary to long established conventions. The whole point of this thread was to point out this dastardly practice.
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TheGodfather234
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Re: Microsoft Algebra Question
« Reply #27 on: Mar 30th, 2005, 7:23pm » |
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-x^4
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SWF
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Take a look at the attached Excel file. Cells A1 and B1 contain the same formula (-2^2), but give different results for the computation (-4 and +4). Why is this? Should I just be satisfied that least one of them is correct this time.
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Icarus
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Re: Microsoft Algebra Question
« Reply #30 on: Apr 5th, 2005, 7:39pm » |
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Now that is truly messed up! How did you manage to accomplish this? If I do any manipulation of the correct formula, it reverts back to the incorrect value, even if I undo the change I made, or the change is not a real change at all (replacing "2" with "2") before pressing "enter". However, I can copy the cell and paste it and still get -4. This holds even if I paste just the formula, not the value.
I would suggest telling MS about it, except that if they did anything, they would surely go the wrong way and have it =4 at all times.
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SWF
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Re: Microsoft Algebra Question
« Reply #31 on: Apr 12th, 2005, 7:28pm » |
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I was using the Linux spreadsheet, Gnumeric (which does arithmetic correctly), and wondered what would happen if saved to Excel format. From Gnumeric I put the formula -2^2 in cell A1, saved as Excel format. Then opened the file in Excel. The formula looked the same as before and even gave the correct answer of -4. Then I typed the same formula in cell B1, which Excel computes incorrectly.
When that file is saved from Excel, and reopened in Gnumeric, the values for the two cells are -4 and +4, but Gnumeric has corrected the formula in B1 with parentheses: (-2)^2.
The spreadsheet in "Open Office" which is meant to be compatible with MS Office does exponents the Microsoft way. Evidently compatiblity with MS was the objective with Open Office, and common sense took precedence with Gnumeric.
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Icarus
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Re: Microsoft Algebra Question
« Reply #32 on: Apr 13th, 2005, 3:55pm » |
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That explains it. Excel (and probably other spreadsheets) includes both the formula and the current value in their cell objects. This saves on the amount of calculation the spreadsheet has to do. The value is only recalculated when the cell formula or one of formula's referenced cells is changed.
Since you had a sane spreadsheet program calculate the value, it was correct, and since Excel did not know the spreadsheet had been created by a sane program, it didn't realize it needed to recalculate for continue attempting to fool the masses.
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I wonder: Which is larger
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SWF
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Re: Microsoft Algebra Question
« Reply #33 on: Apr 13th, 2005, 7:19pm » |
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In Excel, there is a "Formula Auditing" option which can be picked from the Tools drop down menu. Using that shows the formula in cell A1 is stored as if operations are done in the standard order, while cell B1 is stored as if done with Microsoft math. So I don't think Excel is saving a computed result. I believe the formula is translated from the typed text and stored in some other format in Excel, and that is what gets preserved. I will try testing it by using a formula referring to cells and then change values in the referenced cells.
If you write -x^y for a formula in a Visual Basic macro, it does the operations in the standard order and therefore gives a different result from the same formula placed in an Excel cell.
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| « Last Edit: Jul 6th, 2005, 5:42pm by SWF » |
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SWF
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Re: Microsoft Algebra Question
« Reply #34 on: Jul 6th, 2005, 5:43pm » |
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Here is another Excel alert:
Today, I noticed that Excel uses the arguments of the atan2() function in an order different from commonly used by computer languages. Most (all?) languages that have the atan2() function use the arguments in the order atan(y,x), but Excel has them reversed as atan2(x,y).
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paul schmitz
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Re: Microsoft Algebra Question
« Reply #35 on: Jul 6th, 2005, 11:05pm » |
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i know that almost all calculators translate -x^2 as -(x^2) and frankly i think it's really annoying. when i write algebra, i use the negative "-" symbol as the highest priority. most calculating systems use "-" to abbreviate *-1, which gives it the same priority as multiplication. it's weird that MS does it differently from everything else, but if i had to choose i think it's more logical to do it their way. of course, since everything else does differently, it's wrong to do it like that.
more often that i'd like, i've hastily plugged in a "-" without the appropriate parenthensis' and i've gotten a wrong answer.
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towr
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Re: Microsoft Algebra Question
« Reply #36 on: Jul 7th, 2005, 1:11am » |
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Yes, really annoying when programs follow mathematical convention..
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Wikipedia, Google, Mathworld, Integer sequence DB
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River Phoenix
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Re: Microsoft Algebra Question
« Reply #37 on: Jul 7th, 2005, 6:21am » |
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paul, what about something written as:
x^3 - 2x^2 + 4
Should that second term be the same as (-2x)^2?
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| « Last Edit: Jul 7th, 2005, 6:23am by River Phoenix » |
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