Geometry

3.14 is the rounded one. 3.14159265359 is more specific. ^_^

You should just write the symbol for pi instead of trying to approximate with a number, because your answer will be more precise.

For example, the area of circle is pi*r^2. Therefore, if the radius is 4, you should just write 16(pi), instead of approximating to 50 (or even 50,26548245743669.)

Yes, Pi is an irrational number which means that it cannot be written exactly as a fraction or a decimal. It cannot even be writtne exactly as a repeating decimal.
The digits after the decimal point just keep going on forever without even forming a pattern.