(a) Show that the limit x*ycosy lim (x.y)(0,0) does not exist. (b) If u = x cos y+ye", wherex=s+2t and y = st, prove that ди ди 2- at = (s – 21) (x² siny- xye" – e"). Let f(x,y) = (x + (5))³....

question b

Extracted text: (a) Show that the limit x*ycosy lim (x.y)(0,0) does not exist. (b) If u = x cos y+ye", wherex=s+2t and y = st, prove that ди ди 2- at = (s – 21) (x² siny- xye" – e"). Let f(x,y) = (x + (5))³. Determine the directional derivative of f at the point (1,0) in the direction of ū = (,). (c)