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August 31st, 2011, 06:51 PM   #1
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I love elitist math textbook authors who don't show you how to do the homework problems in the examples.

Anyways, I'm seeing problems like this come up in the homework for degrees minutes seconds (dms) and decimal degrees (dd). I have to convert, for example, -57.68 deg to degrees minutes seconds. My answers are coming out off from the ones in the back of the book.

For example, -45 deg 6' is, somehow, -44.9 dd? Okay, if I write the problem like this: -45 deg + 6/60' = -45 deg + 0.1 deg = -44.9 dd then it makes sense. However, when I take it back the other way (to dms), I'm screwing something up. In this case...

-44.9 deg = -44 deg + 0.9(60') = -44 deg + 54' = -43 deg 6' != -45 deg 6' What am I doing wrong with this relatively simple calculation?

Last edited by skipjack; April 16th, 2015 at 06:19 PM.
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August 31st, 2011, 07:05 PM   #2
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Re: Trig: Converting negative decimal degrees to deg/min'sec

-44.9 = -(44 +9/10) = -(44 +54/60) = -44 - 54' = -45 6'.
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August 31st, 2011, 08:25 PM   #3
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Re: Trig: Converting negative decimal degrees to deg/min'sec

Alright, I follow you there - I'm supposed to negate ALL the elements of the dms figure. So, say -60deg50'20" = -60deg - 50' - 20" is correct?

Also, if that's how it works, how is the initial conversion correct? or is it? So...
-45 deg 6' = -45 deg + 6/60' = -45 deg + 0.1 deg = -44.9 dd should be
-45 deg 6' = -(45 deg + 6/60') = -(45deg + 0.1 deg) = -45deg - 0.1 deg = -45.1 dd != 44.9 dd

What did I just do wrong there?
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September 1st, 2011, 05:49 AM   #4
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Re: Trig: Converting negative decimal degrees to deg/min'sec

You're using different negative/positive values.

-45 deg 6' = -(45 deg - 6/60') = -(45deg - 0.1 deg) = -45deg + 0.1 deg = -44.9 dd

or

-45 deg 6' = -45 + 6/60 = -45 + 1/10 = -44.9 dd.

They're using different signs for deg and ' (and that seems unusual).
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September 1st, 2011, 09:44 AM   #5
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Re: Trig: Converting negative decimal degrees to deg/min'sec

The deg is because I'm new to this site and I'm too lazy to hunt around in character map for the actual degree symbol. Thanks for the help, Greg!
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April 16th, 2015, 01:26 PM   #6
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-44=.9 deg = -44deg - .9(60)' etc. You had + instead of -.
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