An ellipsoid is given by
It is cut by the plane
Find the volume of the region that is inside the ellipsoid and below the plane. It is assumed that the upward direction is along the positive -axis. This 3D region is depicted in the figure above.
If the volume is , enter as your answer.
Hint : Use scaling to transform the ellipsoid and the cutting plane into a sphere with a corresponding cutting plane.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
We start by transforming the given ellipsoid into the unit sphere (radius 1)
Define x ′ = x / 1 0 , y ′ = y / 1 5 , z ′ = z / 3 0 , then
x ′ 2 + y ′ 2 + z ′ 2 = 1
The corresponding cutting plane, is derived by substituting x, y, z into its equation
( 1 0 x ′ ) + 3 ( 1 5 y ′ ) + 2 ( 3 0 z ′ ) = 4 0
or
1 0 x ′ + 4 5 y ′ + 6 0 z ′ = 4 0
which simplifies to
2 x ′ + 9 y ′ + 1 2 z ′ = 8
This plane cuts through the sphere. The distance from the center of the sphere is
a = 2 2 + 9 2 + 1 2 2 8 = 2 2 9 8
Now we use the following formula for calculating the volume of a cut sphere of radius R, with
a plane that is a distance a away from the center.
V S = π { 3 2 R 3 + a R 2 − 3 a 3 }
Substituting the calculated a , and R = 1 , results in
V S = 1 . 1 4 6 0 7 2 7 6 π
Finally we scale back this volume, to get the volume of the cut ellipsoid
V = ( 1 0 ) ( 1 5 ) ( 3 0 ) V S = 1 6 2 0 2 . 2 2 2 , therefore the answer is ⌊ 1 6 2 0 2 . 2 2 2 ⌋ = 1 6 2 0 2 .