D1.2. A vector field S is expressed in rectangular coordinates as S = (125/ [(x-1)²+(y-2)²+(z+1)]]{(x-1)a, +(y-2)ay +(z+1)a). (a) Evaluate S at P(2, 4, 3). (b) Determine a unit vector that gives the direction of S at P. (c) Specify the surface f(x, y, z) on which |S| = 1. Ans. 5.95a, +11.90ay + 23.8az; 0.218a, +0.436a, +0.873a; √(x-1)²+(-2)² + (z+1)² = 125