[Zope] Square Roots... Please help sqrt(x)

To anyone who may be able to help, I need to calculate the distance between two zip codes and all is working except for the square root part. I have been trying to use <dtml-var expr="_.sqrt(x)"> to get the square root of x. But it does not work and reports an attribute error. I have used the _.int(x) with no problem and dis notice the sqrt() is in the Math Library. Is there additional syntax to access this function? I searched and googled and found everything but an example in DTML of how to use sqrt(). Thanks, Richard