1.9

first.erl

%% @doc Function for calculating area of any triangle and some auxiliary
%% functions

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

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

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

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

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

%% @doc Area of a triangle with sides A, B, and C

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