I need to write this:

f(x,y) = hardlim(sqrt(x^2+y^2)-1) (hardlim(x) = 0 if x <= 0 and 1 otherwise)

but without using any multiplication or the square root. Only thing I can use is summation, multiplication by a value (x*5), and the hardlim or hyperbolic tangent functions.

(I basically need to build a neural net classifier thingie that will return 1 if a point is in the unit circle and 0 otherwise.)