This page has two versions of the Law of Cosines as programs for your TI-83 or 84 calculator. The programs are very short and given here:
Here is a TI-83 calculator
program
to do the Law of Cosines (SAS version to solve
for
the opposite side). Program 1:
Hit PRGM
Follow
each line here with ENTER.
Comments
you do not type are in black.
Go to NEW
Enter the name, letter by letter,
say, LAWCOS
(the blinking "A" means Alphabetic
mode which refers to the letters in green on your keyboard. Otherwise, to enter "D" hit "ALPHA (a green key) D")
Name: LAWCOS
Prompt A,B,C
sqrt(A2 + B2
- 2*A*B*cos(C)) -> D
Disp D
[In the above, "sqrt" means the square root key, and
"->"
is the arrow or "STOre" key.]
In the above program A and B are adjacent sides and C
is the included angle. D is the opposite side.
Keystroke details:
1) Hit "PRGM"
2) go to "NEW" and hit "ENTER"
3) Type in a name, say, "LAWCOS"
and ENTER
4) Find the "Prompt" command by hitting "PRGM"
[again], arrow over to "I/O" (input/output), arrow down to "Prompt" and
hit ENTER.
5) Type in "A,B,C"
[Use the alpha key to use the alphabet. There is a comma key]
6) Type in the formula (above)
7) "Display" the result (D) by typing PRGM, I/O
and selecting "Disp" and alpha D
8) Quit and run it on a problem where you know
the answer, to check it.
(Reproduce one of the calculations in the text.)
Program 2: To use the Law of Cosines to solve for an angle, use this program (short!):
COSANG
Prompt A,B,C
cos-1((C2-A2-B2)/(-2*A*B))
-> E
Disp E