+- HP Forums (https://www.hpmuseum.org/forum)
+-- Forum: Not HP Calculators (/forum-7.html)
+--- Forum: Not remotely HP Calculators (/forum-9.html)
+--- Thread: Retina display math (/thread-517.html)
Retina display math - Joe Horn - 01-25-2014 10:00 PM
In the Wikipedia article about "Retina Display", in the second paragraph of the "Technical definition" section, it has this phrase (DEGREE MODE is assumed):
"twice the Tan of π divided by 360 (equal to half a degree in radians)"
A few lines later it says:
"Two times the Tan of π divided by 360 can also be approximated with π divided by 180 (= 0.01745)."
Am I going senile, or are these statements mathematically whacked? According to all my HP calculators, in degree mode:
2*tan(pi)/360 = tan(pi)/180 = 0.000304923...
0.5 degrees = 0.008726646... radians
pi/180 = 0.01745329...
The article claims that the first two are equal, and that the first and third are approximately equal. But they're orders of magnitude apart. What's going on here?
It's not a degree mode versus radian mode thing. In radian mode, the first is zero and the other two remain unchanged.
EDIT: Oh, sorry, false alarm. They forgot to put parentheses around "pi divided by 360", and then it all works ok in radian mode, even though the article is entirely about degrees. Sheesh.
RE: Retina display math - Han - 01-25-2014 10:31 PM
\( 2\tan(\pi/360) \) since \( \pi/360 \) radians is half a degree
RE: Retina display math - Joe Horn - 01-26-2014 04:59 AM
(01-25-2014 10:31 PM)Han Wrote: \( 2\tan(\pi/360) \) since \( \pi/360 \) radians is half a degree
That's what alerted me to the missing parentheses: their mention of "half a degree in radians". I'm so accustomed to the "order of operations" rule that at first I just blindly did exactly what they said, without thinking. Lesson learned.