Wikipedia picture of the day on January 5, 2019: Circular...
Wikipedia picture of the day on January 5, 2019: Circular paraboloid generated by
z
=
−
a
(
x
2
+
y
2
)
,
a
>
0
{\displaystyle z=-a(x^{2}+y^{2}),a>0}
.
from Tumblr http://bit.ly/2F9JB8m
via Tumblr