Question

I am asked to show that f(x,y,z) =(x²+y²+z²)^-1/2satisfies the Laplace equation(δ²f/δx²)+(δ²f/δy²)+(δ²f/δz²)=0I only want help finding δf/δx and δ²f/δx²,so I can work the rest by myself. I am either doing the derivativeswrong or this equation doesn't satisfy Laplace, because when I workthis problem I don't get 0.