Functional programming in Erlang course

first.erl

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

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

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

treble(X) ->
  mult(3,X).

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

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

second.erl

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

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

%% Perimeter of a right-angled triangle
perimeter(A,B) ->
  A+B+(hypotenuse(A,B)).

%% Area of a right-angled triangle
area(A,B) -> A*B/2.