Ineed finding the vertical distance problem 5(c)

Find the gradient of f(x, y,z)equals=left parenthesis x squared plus y squared plus z squared right parenthesis superscript negative 1 divided by 2 baseline plus ln left parenthesis x right parenthesis x2+y2+z2−1/2+ln(xyz) at the point left parenthesis negative 2 comma 1 comma negative 2 right parenthesis(−2,1,−2).

Complete the standard form of the equation that represents the quadratic relationship displayed above, where a, b, and c are rational numbers.

The sum of two numbers is 12 and their difference is 18 what are the two numbers