Solution for the first assignment

first.erl

-module(first).

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

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

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

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

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

% caluculate the hypotenuse of a right-angled triangle
% C^2 = A^2 + B^2
hypotenuse(A, B) ->
    math:sqrt(first:square(A) + first:square(B)).

% calculate the perimeter of a right-angled triangle
% perimeter = A + B + C (hypotenuse(A,B))
perimeter(A, B) ->
    A + B + hypotenuse(A, B).

% calculate the area of a right-angled triangle
% area = 1/2 * (A * B)
area(A, B) ->
    0.5 * (A * B).

Great solution.
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