Where to get and how to connect the Math library to Ruby?

Question

ruby

require 'mathn'

puts Math.sqrt(4 / 9)

Answer 1

Math should be enabled by default,
You can check in IRB:

> irb
2.4.3 :001 > Math # без require
 => Math
2.4.3 :002 > Math.sqrt 4
 => 2.0