我可以这样写：Math :: sin,Math :: PI或Math.sin,Math.PI？
puts Math::PI #=> 3.141592653589793 include Math puts PI.class #=> Float require "bigdecimal/math" include BigMath puts PI(50).class #=> BigDecimal puts PI(50) #=> 0.3141592653589793238462643383279502884197169399375105820974944592309049629352442819E1
