1. Using PHPTester, design a function that allows you to calculate the area of a triangle, a square and a circle, consider all the necessary variables and declare them with test values to execute the function and get the 3 areas on the screen configured. 2. When using variables and functions in PHP mention what extensions and what classes and interfaces recognizes as part of the language. 3. From the native functions available in PHP, select 5 and test them in PHPTester