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[DPRG] math I once knew

Subject: [DPRG] math I once knew
From: Sluggy! slugmusk at linuxlegend.com
Date: Fri Dec 20 16:59:00 CST 2002

I knew it would be pretty simple and infact, I'd tried the very solution 
as Kip presented it:

radius * sin(angle) = Y
radius * cos(angle) = X

For my example, I used a radius of 3" and using Excel, I calculated the 
coordinates for each point along the clock face for the first 15 minutes.

There is, however, a problem with the numbers.

hour 
min 
radius 
deg 
X 
	Y
					
12 
0 
3 
0 
3 
	0
	1	3	6	2.88051086	-0.838246495
	2	3	12	2.531561876	-1.609718754
	3	3	18	1.980950125	-2.25296174
	4	3	24	1.272537022	-2.716735086
1 
5 
3 
30 
0.46275435 
-2.964094872
	6	3	36	-0.383891069	-2.97533656
	7	3	42	-1.199955945	-2.749564644
	8	3	48	-1.920433018	-2.304763984
	9	3	54	-2.487929499	-1.676367147
2 
10 
3 
60 
-2.857238941 
-0.914431863
	11	3	66	-2.998942368	-0.079653462
	12	3	72	-2.901751765	0.761470088
	13	3	78	-2.57340928	1.541935368
	14	3	84	-2.040070487	2.19957096
3 
15 
3 
90 
-1.344220848 
2.681989991


If you look at these, 0 degrees works out fine, corresponding to the 3 
o'clock position as given. Then the points run clockwise from 3 o'clock 
all the way to about 11 o'clock. I would have expected 90 degrees to end 
up at 6 o'clock, with X = 0 and y = -3, but even the closest value (36 
degrees) isn't exactly 6 o'clock.

The formulae in Excel are

X = radius * COS(deg)
Y = radius * SIN(deg)

with relative cell addresses rather than values, of course.

Any ideas what I'm skipping?

Sluggy!


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