1. Use polar coordinates to find the limit. [Hint: Let x=r cos and y=r sin , and note that (x,y)(0,0) implies r0.]

• lim(x,y)(0,0)x2+y2x2y2

2. Find dw/dt (a) by using the appropriate Chain Rule and (b) by converting w to a function of t before differentiating.

• w=cos(xy),x=t2,y=1

3. To find the directional derivative of the function at P in the direction ofPQ

• f(x,y)=cos(x+y),P(0,),Q(2,0)