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

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

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

% Area of a triangle (Heron's formula)
area(A,B,C) ->
    S = (A+B+C)/2,
    math:sqrt(S*(S-A)*(S-B)*(S-C)).

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

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