FutureLearn - Erlang - 1.9

first.erl

-module(first).
-export(
   [
	double/1,
	mult/2,
	area/3,
	square/1,
	treble/1
   ]
  ).

mult(X,Y) ->
	X*Y.

double(X) ->
	mult(2,X).

area(A,B,C) ->
	S = (A+B+C) / 2,
	math:sqrt(S * (S-A) * (S-B) * (S-C)).

square(X) ->
	mult(X,X).

% Meaning "triple" for british people, learned a new word!
treble(X) ->
	mult(3,X).

second.erl

-module(second).
-export(
   [
	hypotenuse/2,
	perimeter/2,
	area/2
   ]
  ).

hypotenuse(A,B) ->
	SUM = first:square(A) + first:square(B),
	math:sqrt(SUM).

perimeter(A,B) ->
	C = hypotenuse(A,B),
	A + B + C.

area(A,B) ->
	first:mult(A,B) / 2.