For f(x,y) = root(25-x^2-y^2) calculate:

a. the values: f(3,4)....easy! Just substitute, need no help here. And gradient f(3,4) = the partial derivatives df/dx and df/dy at the value 3,4...need help here. And finally the Hessian H (3,4) which is a matrix of second partial derivatives and the values need to be plugged in.

While calculating the partial derivatives I get strange numbers or the answer 0 in every case. I don't think the answer is a matrix of zeros but the strange numbers I get if I do something else don't make much sense either.

Try to tell me what to do.

Thanks.