Graficar las curvas de nivel, para z = –2, z = –1. z = 0, z = 1, z = 2, de las siguientes superficies

a) ∃/ ∃/ 022 =+ yx 122 =+ yx 222 =+ yx
b) 12 −−= xy 2 1 2 −−= xy 0=y 2 1 2 += xy 12 += xy
c) 2 2 −−= xy 32 −−= xy ∃/ 12 += xy 2 2xy =
d) 4 1 2 1 2 =++ yx ( ) 11 22 =++ yx 0=x ( ) 11 22 =+− yx 4 1 2 1 2 =+− yx
e) 12 2 −−= xy 2xy −= 1=y 22 += xy 32 2 += xy
f) 2−−= xy 1−−= xy xy −= 1+−= xy 2+−= xy
g) ∃/ ∃/ 1−−= xy xy −= 3+−= xy
h) 1−=xy 2 1−=xy = 0 0 y x 2 1=xy 1=xy