input a number (x) and create a program that allows the user to select finding the area (Area) of one of the the following.

- The Area of a Square with the side x, Area = x * x

- The Area of a a circle with radius x, Area = 3.14 * x^2

- The area of an equilateral triangle with side x, Area = sqrt(3)/4 * x^2

Note: Because x represents a dimension, we require that x > 0. Be sure to include this requirement in your program.