
Section 6: Functions91




In the HP41C, trigonometric functions assume angles in decimal degrees,
decimal radians, of decimal grads. If you want to use any trigonometric
functions on angles given in degrees, minutes, seconds, you must
first convert the angle to decimal degrees.


Example: Lovesick sailor Oscar Odysseus
dwells on the island of Tristan da Cunha
(37 ° 03′S, 12° 18′W), and his
sweetheart, Penelope, lives on the nearest island.
Unfortunately for the course of true love, however,
Tristan da Cunha is the most isolated inhabited spot
in the world. If Penelope lives on the island of St.
Helena (15° 55′S, 5° 43′W), use
the following formula to calculate the great circle
distance that Odysseus must sail in order to court her.







Distance

=

cos ^{–1} [ sin (LATs)
sin (LATd) +
cos (LATs)
cos (LATd)
cos (LNGd –
LNGs)] × 60




Where:



LATs and LNGs =
latitude and longitude of the source (Tristan da Cunha).


LATd and LNGd =
latitude and longitude of the destination (St. Helena).



Solution: Convert all degrees, minutes, seconds entries into
decimal degrees as you key them in. The equation for the great circle distance
from Tristan da Cunha to the nearest inhabited land is:



Distance

=

cos ^{–1} [ sin (37° 03′)
sin (15° 55′) +
cos (37° 03′)
cos (15° 55′)
cos (5° 43′W –
12° 18′W)] × 60




Since the HR function is still assigned to
the ex key location, simply switch
to USER mode.
