Which of the following functions f(x,y)f(x, y)f(x,y) satisfies the Laplace equation ∇2f=fxx+fyy=0\nabla^2 f = f_{xx} + f_{yy} = 0∇2f=fxx+fyy=0?
f(x,y)=x2+y2f(x, y) = x^2 + y^2f(x,y)=x2+y2
f(x,y)=x2−y2f(x, y) = x^2 - y^2f(x,y)=x2−y2
f(x,y)=exf(x, y) = e^xf(x,y)=ex
f(x,y)=sin(x)+sin(y)f(x, y) = \sin(x) + \sin(y)f(x,y)=sin(x)+sin(y)