Determine how many different computer passwords are possible if: (a) digits and letters can be repeated, and (b) digits and letters cannot be repeated. 1. 3 digits followed by 4 letters.
2. 2 digits followed by 5 letters.

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).