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6049 Volume
AP Calculus
Volume
Volume = the sum of the quantities in each layer
๐โ๐คโh
where h is # layers
x
x
y
xx
x-axis
Volume by Cross Sections
n
( )x thickness h
foundation
BE7250
Axial (cross sectional) magnetic resonance image of a brain with a large region of acute infarction, formation of dying or dead tissue, with bleeding. This infarct involves the middle and posterior cerebral artery territories.Credit: Neil Borden / Photo Researchers, Inc.
Volume by Slicing(Finding the volume of a solid built on the base in the x โ y plane)
METHOD:
1.) Graph the โBASEโ
2.) Sketch the line segment across the base.
That is the representative slice โnโ
Use โnโ to find: a.) x or y (Perpendicular to axis)
b.) the length of โnโ
3.) Sketch the โCross Sectional Regionโ - the shape of the slice (in 3-D )
from Geometry V = B*h h = or is the thickness of the slice
B = the Area of the cross section
4.) Find the area of the region
5) Write a Riemannโs Sum for the total Volume of all the Regions
โ ๐ฅ ๐๐๐๐๐๐ข
๐๐๐๐๐๐๐
Example 1: The base of a solid is the region in the x-y plane bounded by the graph
and the y โ axis. Find the volume of the solid if every cross section by a plane perpendicular to the x-axis is a square.
2 3x y
Base
Cross -Section
x
y
๐ฆ 2=3 โ๐ฅ๐ฆ=ยฑโ3 โ๐ฅ
๐๐= lim๐โ โ
โ0
3
(2โ3 โ๐ฅ )2 โ ๐ฅ
โซ0
3
(2โ3 โ๐ฅ )2๐๐ฅ
๐ฆ=โ3 โ๐ฅ
๐ฆ=โโ3โ ๐ฅ
h
๐=(โ3โ๐ฅ ) โ (โโ3โ๐ฅ )
๐=2โ3 โ๐ฅ๐=๐ตโh๐=๐2 โ๐ฅ๐= (2โ3โ๐ฅ )2
โ ๐ฅ
Example 2: The base of a solid is the region in the x-y plane bounded by the graph
and the y โ axis. Find the volume of the solid if every cross section by a plane perpendicular to the x-axis is an Isosceles Rt. Triangle (leg on the base).
2 3x y
x
y
nn ๐=๐ตโh
๐=12
(๐2 ) โ ๐ฅ
๐ฆ=โ3 โ๐ฅ
๐ฆ=โโ3โ ๐ฅ
h
๐=(โ3โ๐ฅ ) โ (โโ3โ๐ฅ )
๐=2โ3 โ๐ฅ
๐๐= lim๐โ โ
โ0
3
( 12
(( 2โ3โ ๐ฅ )2 ))โ๐ฅ
โซ0
3
( 12
( (2โ3โ๐ฅ )2 ))๐๐ฅ
Some Important Area Formulas
Square-
side on base
Square-
diagonal on base
Isosceles rt ฮ
leg on base
Isosceles rt ฮ
hypotenuse on base
Equilateral ฮ
Semi - Circle Circle
diameter on the base
๐ต=๐2
n
nnn
n
n
n
๐ต=๐2
2
๐ต=12๐2
๐ต=๐2
4
๐2
โ3๐ต=1
2๐(๐2 )โ3
๐ต=๐2
4โ3
๐ต=๐ ๐2
4๐ต=1
2 (๐2 )2
๐
๐ต=๐ ๐2
8
EXAMPLE #4/406The solid lies between planes perpendicular to the x - axis at x = -1 and x = 1 . The cross sections perpendicular to the x โ axis are circular disks whose diameters run from the parabola y = x2 to the parabola y = 2 โ x2.
๐ฅ2=2 โ๐ฅ2
2 ๐ฅ2=2๐ฅ2=1๐ฅยฑโ1
๐=โ ๐ฅ [โ 1,1 ]๐=(2โ๐ฅ2 ) โ (๐ฅ2 )๐=2 โ2 ๐ฅ2n
๐=๐ตโh
๐= ๐๐2
4โ ๐ฅ
๐=๐4
(2 โ2 ๐ฅ2 )2 โ๐ฅ
๐๐= lim๐โ โ
โ ๐4
(2 โ2๐ฅ2 )2โ ๐ฅ
๐๐=โซ ๐4
(2 โ2 ๐ฅ2)2๐๐ฅ
๐๐=๐4 โซ ( 4 โ 8๐ฅ2+4 ๐ฅ4 )๐๐ฅ
The base of a solid is the region bounded by The cross sections, perpendicular to the x-axis, are rectangles whose height is 3x
4=๐ฅ2
ยฑ 2=๐ฅ
h=โ๐ฅ [โ 2,2 ]๐=4 โ๐ฅ2
๐=๐ตโh๐= [ ( 4โ๐ฅ2 ) 3๐ฅ ] โ ๐ฅ
lim๐โ โ
โ [ (12 ๐ฅโ 3๐ฅ3 ) ] โ๐ฅ
โซ [ (12๐ฅโ3 ๐ฅ3 ) ]๐๐ฅ
Assignment:
P. 406 # 1 - 6 all If the problem has multiple parts work โ a โ then set up only ( to the definite integral) the other parts.
Volumes of Revolution:
Disk and Washer Method
AP Calculus
Volume of Revolution: Method Lengths of Segments:In revolving solids about a line, the lengths of several segments are needed for the radii of disks, washers, and for the heights of cylinders.A). DISKS AND WASHERS 1) Shade the region in the first quadrant (to be rotated) 2) Indicate the line the region is to be revolved about.
3) Sketch the solid when the region is rotated about the indicated line.4) Draw the representative radii, its disk or washer and give their lengths.<<REM: Length must be positive! Top โ Bottom or Right โ Left >>
Ro = outer radius
ri = inner radius
Disk MethodRotate the region bounded by f(x) = 4 โ x2 in the first quadrant about the y - axis
The region is _______________ _______ the axis of rotation.
The Formula: The formula is based on the
_____________________________________________
adjacent to
Volume of a cylinder
๐=๐ ๐2 h
h=โ ๐ฆ [ 0,4 ]๐=โ4 โ๐ฆโ 0
Right-left
๐ฆ=4 โ๐ฅ2
4 โ ๐ฆ=๐ฅ2
ยฑโ4 โ๐ฆ=๐ฅ
๐โซ (โ4 โ๐ฆ )2๐๐ฆ
Washer MethodRotate the region bounded by f(x) = x2, x = 2 , and y = 0 about the y - axis
The region is _______________ __________ the axis of rotation.
The Formula: The formula is based on
_____________________________________________
Separate from
Big cylinder-small cylinder
๐=๐ ๐ โ2 hโ๐๐ 2h
๐ (๐ 2 โ๐2 ) h
lim๐โ โ
โ ๐ ( (2 )2โ (โ๐ฆ )2 )โ ๐ฆ
h=โ ๐ฆ [ 0,4 ]๐ =2 โ0๐=โ๐ฆโ 0
๐โซ0
4
( 4 โ ๐ฆ )๐๐ฆ
๐=8๐
Disk MethodRotate the region bounded by f(x) = 2x โ 2 , x = 4 , and y = 0 about the line x = 4
The region is _______________ _______ the axis of rotation.Adjacent to
๐ท๐๐ ๐๐ ๐2 h ๐ฆ=2 ๐ฅโ2
๐ฅ=๐ฆ+2
2โ ๐ฆ [ 0,6 ]
๐=4 โ( ๐ฆ+22 )
๐=4 โ12๐ฆโ 1
๐=(3 โ12๐ฆ )
๐=13๐๐2 h
๐=13๐ (3 )2 (6 )
๐=18๐
๐โซ0
6
(3 โ12๐ฆ )
2
๐๐ฆ
Washer Method
Rotate the region bounded by f(x) = -2x + 10 , x = 2 , and y = 0 about the y - axis
The region is _______________ __________ the axis of rotation.Separate from
๐ฆ=โ 2๐ฅ+10
๐ฅ=5โ12๐ฆ
๐ =5 โ12๐ฆ
๐=2
h=โ ๐ฆ [ 0,6 ]๐ (๐ 2 โ๐2 ) h
lim๐โ โ
โ ((5 โ12๐ฆ )
2
โ (2 )2)โ ๐ฆ
V=
Separate
Example 1:
The region is bounded by Rotated about:
the x-axis, and the y-axis a) The x-axis
b) The y-axis
c) x = 3
d) y = 4
24y x
Example 2:
The region is bounded by: Rotated about:
f(x) = x and g(x) = x2 a) the x-axis in the first quadrant b) the y-axis
c) x = 2d) y = 2
Example 2: The base of a solid is the region in the x-y plane bounded by the graph
and the x โ axis. Find the volume of the solid if every cross section by
a plane perpendicular to the x-axis is an Isosceles Rt. Triangle (leg on the base).
2 3x y