math - Using Ruby's log with 2 Arguments -

i'm using ruby math.log function , passing 2 arguments , i'm getting sort of error that.

puts math.log(10, 10) 

the error get:

log': wrong number of arguments (2 1) (argumenterror) 

the docs that's how it's supposed work?

http://www.ruby-doc.org/core-2.0/math.html#method-c-log

i take bet , suggest using ruby 1.8.7 in math.log takes 1 argument.