[DOC] rational and imaginary literals [ci skip]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65773 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

doc/syntax/literals.rdoc

@@ -71,6 +71,33 @@ Examples:
 All these numbers have the same decimal value, 170.  Like integers and floats
 you may use an underscore for readability.
 
+=== Rational numbers
+
+Numbers suffixed by +r+ are Rational numbers.
+
+  12r         #=> (12/1)
+  12.3r       #=> (123/10)
+
+Rational numbers are exact, whereas Float numbers are inexact.
+
+  0.1r + 0.2r #=> (3/10)
+  0.1 + 0.2   #=> 0.30000000000000004
+
+=== Complex numbers
+
+Numbers suffixed by +i+ are Complex (or imaginary) numbers.
+
+  1i          #=> (0+1i)
+  1i * 1i     #=> (-1+0i)
+
+Also Rational numbers may be imaginary numbers.
+
+  12.3ri      #=> (0+(123/10)*i)
+
++i+ must be placed after +r+, the opposite is not allowed.
+
+  12.3ir      #=> syntax error
+
 == Strings
 
 The most common way of writing strings is using <tt>"</tt>: