The answer I got was by first finding the partial derivative with respect to r which I found to be 2r/(r^2 + s) and then I squared it and got 4r^2/(r^2 + s)^2 I plugged this into wolfram alpha and it gave a different answer, can someone explain what I'm doing wrong?
Original Question (Number 2)
The second order derivative does not mean "take the derivative and square the result". The notation actually means "take the derivative, and then take the derivative of your result".