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Wrong answer when evaluating log(10^-12)
Message #1 Posted by Daniel Greenidge on 26 Jan 2012, 10:53 a.m.

Hello everyone,

I know from the power property that log(10^-12) should be -12. Wolfram-Alpha corroborates this.

However, when I evaluate this on both my HP 15C and 50g, the answer turns out to be -11. Here are the exact keystrokes I am using for my 15C:

10 EEX 12 CHS g LOG

Any ideas why this might be?

Thank you, Daniel

      
Re: Wrong answer when evaluating log(10^-12)
Message #2 Posted by Bart (UK) on 26 Jan 2012, 11:09 a.m.,
in response to message #1 by Daniel Greenidge

Hint:

You will get the right answer if you do:
10 ENTER 12 CHS YX g LOG

Regards

Edit: I should rather have said: "expected answer" above.

As Gerson says below, the answer you got is right too, to put it another way: EEX represents "10^" so 10 EEX x = 10 x 10^x = 10^(x+1)

Edited: 26 Jan 2012, 11:26 a.m.

            
Re: Wrong answer when evaluating log(10^-12)
Message #3 Posted by Gerson W. Barbosa on 26 Jan 2012, 6:53 p.m.,
in response to message #2 by Bart (UK)

Quote:
As Gerson says below, the answer you got is right too,

Bart,

I hadn't read your post yet when I said the answer of the calculator was right. "Expected answer" appears to be a more didactic expression, I should have used it myself. By the way, my HP-15C gave a lot of "wrong answers" to me, especially in the beginning, when it was just replacing a TI-59. Oh, and more recently, just some threads below my HP-42S was refusing to give me the answers I expected :-)

Regards,

Gerson.

Edited: 26 Jan 2012, 6:53 p.m.

      
Re: Wrong answer when evaluating log(10^-12)
Message #4 Posted by Gerson W. Barbosa on 26 Jan 2012, 11:18 a.m.,
in response to message #1 by Daniel Greenidge

Quote:
10 EEX 12 CHS g LOG

The answer is right. The input is wrong. You're actually entering 10*10 -12, that is, 101 * 10 -12 = 101-12 = 10-11

Enter the mantissa first, then press EEX and enter the exponent:

1
EEX
12
CHS
g LOG

When the mantissa is 1, it can be omitted.

Gerson.

      
Re: Wrong answer when evaluating log(10^-12)
Message #5 Posted by Daniel Greenidge on 26 Jan 2012, 5:54 p.m.,
in response to message #1 by Daniel Greenidge

Thank you for your help! I feel a bit imbecilic right now but I certainly shall not repeat my mistake.

Regards, Daniel

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