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HP Prime oddity - Richard Berler - 09-20-2013

I set up in textbook mode the integral of 1/sqrt(2*x-x^2) expecting arcsin (x-1).

Instead, I get a convoluted answer with imaginary numbers when using none for simplification. Same for minimum simplification. The real oddity is that it reboots if I try the integral in maximum simplification mode.

Any thoughts?

Re: HP Prime oddity - Gilles Carpentier - 09-20-2013

What rev ?

I get ASIN(x-1) even with 'no simplification' mode

Re: HP Prime oddity - Richard Berler - 09-20-2013

I was inadvertently in complex mode (thought that I had turned it off!). All is good. Phew!

Re: HP Prime oddity - kris223 - 09-20-2013

I get ASIN(x-1) as well, but it seems weird to me.

In textbook mode, I have to use CAS and ' ' with ()'s marks to get the answer.


like that. It then returns ASIN(x-1). If I don't use the extra syntax and just enter it, like in the manual, it returns +/- infinity.

If I'm not in CAS mode it returns Inf without the extra syntax, and with it I get Inf as well.

If I differentiate, it take it like it shows in the manual. diff(x^2) returns 2*x in CAS mode, but returns 0.0000 otherwise.

Kind of new to this though ....

Edited: 20 Sept 2013, 11:43 p.m.

Re: HP Prime oddity - kris223 - 09-20-2013

I think this is so that it doesn't interpret the variable ... like collect(x^2-4). That's the example in the manual but it will return -4 as when I enter x to see what the variable is its 0. If I enter collect('x^2-4') it returns (x-2)*(x+2)

I clearly have some learning to do. I'd think it would know its in some sort of symbolic mode as that's the point of most of these functions and if not why isn't it consistent like diff(x^2) works fine without the extra syntax. Any help would be great.

Edited: 20 Sept 2013, 11:56 p.m.

Re: HP Prime oddity - kris223 - 09-21-2013

OK, so I've learned something new. This may help someone else or you may say I'm seriously in need of help as this is obvious, but either way here it goes :)

The reason why I was having to use quotes is because I assigned a value to x. The quotes did stop the function for evaluating the variable and in fact all I had to do was use 'x' instead of quoting the whole expression. Home based variables use capital letters and the CAS uses lower case letters. Somewhere in my explorations, I set x to a value (either with STO or x:=someNum I guess). Once I did that, the CAS uses that value in the calculation. I had to go VAR key, User tab, User Variables, select x and then use Shift Del key to delete the variable and then! everything was back to normal when I enter int(1/sqrt(2*x-x^2)) it returns ASIN(x-1) ... I'm so glad I figured that out as it was driving me nuts.