first.erl

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

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

square(X) ->
  X*X.

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

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

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