Try these as Google searches to see 3-D graphs of the functions.

Try these as Google searches to see 3-D graphs of the functions. The tanh() one is the best. I also like “1/x+1/y from -20 to 20”

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sqrt(x*x+y*y)+3*cos(sqrt(x*x+y*y))+5 from -20 to 20

sin(5.5x)*cos(5*y)+x*x+1 x is from -1 to 1, y is from -1 to 1, z is from 0.1 to 2.8

tanh(y(y^4+5x^4-10(x^2)(y^2))/(x^2+y^2)^4)