Which of the following functions f(x,y)f(x, y)f(x,y) satisfies the Laplace equation fxx+fyy=0f_{xx} + f_{yy} = 0fxx+fyy=0?
f(x,y)=x2+y2f(x, y) = x^2 + y^2f(x,y)=x2+y2
f(x,y)=excos(y)f(x, y) = e^x \cos(y)f(x,y)=excos(y)
f(x,y)=x2−y2f(x, y) = x^2 - y^2f(x,y)=x2−y2
f(x,y)=x3+y3f(x, y) = x^3 + y^3f(x,y)=x3+y3