There are a few tricks you could use, arranged here in order of increasing trickery.
Logarithms
Observe that k * k = e^log(k*k) = e^(log(k) + log(k))
, and use that rule:
Math.exp(Math.log(5.2) + Math.log(5.2))
# => 27.04
No multiplication here!
Division
As another commenter suggested, you could take the reciprocal operation, division: k/(1.0/k) == k^2
. However, this introduces additional floating-point errors, since k / (1.0 / k)
is two floating-point operations, whereas k * k
is only one.
Exponentiation
Or, since this is Ruby, if you want exactly the same value as the floating-point operation and you don't want to use the multiplication operator, you can use the exponentiation operator: k**2 == k * k
.
Call a web service
It's not multiplying if you don't do it yourself!
require 'wolfram' # https://github.com/cldwalker/wolfram
query = 'Square[5.2]'
result = Wolfram.fetch(query)
Blatant cheating
Finally, if you're feeling really cheap, you could avoid actually employing the literal "*" operation, and use something equivalent:
n = ...
require 'base64'
n.send (Base64.decode64 'Kg==').to_sym, n # => n * n