Y 0 44 let f: r2> r be defined by f(x, y) = y = 0 nere if the directional derivative of f at (0, 0) exists along the direction cos o i +sin a j, where sin a 0,

y 0 44 Let f: R2> R be defined by f(x, y) = y = 0 nere If the directional derivative of f at (0, 0) exists along the direction cos o i +sin a j, where sin a 0, then the value of cot a is .