|Re: Help with HP15C|
Message #5 Posted by Vieira, Luiz C. (Brazil) on 25 May 2005, 2:29 p.m.,
in response to message #4 by Pamela Murray
the small 'c' in the display means your HP15C is ready to calculate with complex numbers, in the form 'a + bi', where 'i' is the square root of (-1). If the 'c' is in the display and you try to compute the square root of (-2), you get no error message and a 0.0000 in the display, meaning the real part of the square root of (-2) is zero, and in this case there is a complex, not-zero component, equal to the square root of 2.
To get rid of the complex mode, locate the  key and check for a [CF] printed in blue, in the slanted face of the key. Now, press:
[g] (AKA: [g][CF])This should de-activate the 'c' indicator and put the HP15C back in real-number mode.
If you want to work with complex numbers again, you can activate the complex mode by using one of the following three sequences:
[f][Re<>Im] (printed in yellow over the [-] key);
[f][I] (printed in yellow, over [TAN] key};
[g][SF] (printed in blue in the slanted face of the  key)
There are some conditions that do not allow complex mode to be activaded: not enough registers available in the common segment (at least five) or having a matrix description in the x-register ([Re<>Im]).
There is a lot more about the HP15C, so if you need help just let us know. One of the guys that constantly declares his acquaintance to the HP15C is Valentin Albillo, an active contributor that has written many good material about it. They are all good choices of reading.
Best regards and success.
Edited: 25 May 2005, 11:44 p.m.