Suppose the temperature at a point in a metal cube is given by T(u, v, w) = 90 - 55e ^[-1/20(u+v +w)] where the centre

Suppose the temperature at a point in a metal cube is given by T(u, v, w) = 90 - 55e ^[-1/20(u²+v² +w²)] where the centre of the cube is taken to be at (1, 0, -2). Find the rate of change of temperature at the origin in the direction of the unit vector. r=(1/?7)(-2,1,-3).