What's the deal with 4xCOS120


This is just an example but why am I getting two different answers here:

4 x COS120 = -0.5


COS120 x 4 = -2 (which is the correct answer)

I am starting to see that this calculator may do me more harm than good.

Edited: 4 Aug 2004, 10:03 p.m.


On my 33S S/N CNA411047XX, I get -2 both ways.

Since the COS of 120 is -0.5, I think perhaps you didn't push = on the first example.


4 x 120 COS = and you'll see -2.


120 COS x 4 = and you'll see -2.

Shows -2 as the solution in the solver too:

4 x COS (120) = X


You don't happen to be a TI user in disguise trying to sow discord here, are you?


The 33s is braindead in alg mode... why on earth is sin postfix?

Even a cheap casio costing 1/3 of the price will accept sin(5)+7! +sqrt(4) = and give the correct answer.

The 33s is an OK RPN calculator, but pretty poor in alg mode compared to the competetion.



Actually, the 33s has three different data entry/interface paradigms:

1.  RPN
2. Equation List --> Algebraic Expression parser
3. ALG --> old style "Algebraic" operation interpreter

Note that the RPN and ALG modes are direct calculation interfaces--not expression parsers--you have the "equation list" for the latter. (It is very unfortunate that the equation feature does not have provision for editing!)

All old style HP, Casio, Sharp, Ti etc etc (including a number of current $15 Casios) "algebraics" work with infix for the basic operations +-x/, and postfix for all "one number" functions. So, I do not think it is right to see this feature as a flaw--it allows one to be efficicent with keystrokes--and to use results for the next computation without having to resort to jumping through hoops, like SIN (2nd ANS) ENTER to get the sin of the last result (this is what you do on a 30s for example).

I think it would have been impossible for the existing RPN-based keystroke programming code to have worked with both RPN and a "direct algebraic logic" type of interface---or it would have been much more difficult at any rate. I would say that it might be worth exploring, though. The way Alg has been implememented on the 33s is fundamentally the same as the 20s and 21s.

Perhaps it is confusing to have the fancy two line diplay show the sin(x) when you have typed x sin.

I think the 33s has bigger problems--the bugs---than whether the ALG interface is perfect.

The real problem with the ALG interface is that there is no good documentation--I have had to discover how LastX, X<>Y etc work, on my own. (And in fact you will see that there are two different implementations of the X<>Y--the newer versions actaully use X<>Y to create a second parallel ALG stack--you can work on two ALG computations at the same time, and tie them together. In fact, you can also use this feature in a program, as a way to implememt a counter or test variable, without having to use any of the letter-named variables:


or the like....



Edited: 5 Aug 2004, 12:50 p.m.


I don't have an HP-30S, but on an HP-33S in ALG mode, I obtain the following results:

press:     4 x 120 COS ENTER 
display: 4xCOS120=

press: 120 COS x 4 ENTER
display: COS120x4=

What's the problem? (other than the unintuitive postfix of unary functions in equation-writing mode...)


Yes, it was a user error. I was not hitting ENTER after entering the numbers. I guess the calculations I made berfore just so happened to give me the correct answer without hitting the ENTER key. But when doing 4 x COS120, I was getting -0.5, which is just the COS120 part, but when doing COS120 x 4, I got the correct answer. Just another little quirk I need to get used to.

And yes, I am a TI user; the 89 and 92+. I still prefer my TI's by far over the hp. No offense.

Anyway, thanks for the info.

Edited: 5 Aug 2004, 11:40 a.m.


<< And yes, I am a TI user; the 89 and 92+. I still prefer my TI's by far over the hp. No offense. >>

None taken. After all, you've implicitly endorsed the HP-33S as the best available calculator in the "NCEES-approved" class. Even though you are a TI user, you still picked the 33S over a host of cheaper NCEES-approved TI models. : )

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