a)
X= cos(u)*3*sin(u)
Y= u
Z= sin(u)*2*cos(u)*3
0 <= u <= 2*pi
b)
X= 1/2*sin(u)*cos(u)
Y= u+sin(u)
Z= 3+sin(u)
0 <=U<= 3*pi
X= sin(v)*cos(v)
Y= 2
Z= v
0 <=V<= 3*pi
