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Polygon
Closed 2-D shape whose sides are segments
Polyhedron
Closed 3-D shape whose faces are polygons (no curves)
Cavaliers’s principle (3D)
If 3D figures have the same height and equal areas everywhere along the height then they have the same volume
(You must know the height of the object and the width along the height, or the base)
Rectangular prism (volume equation)
lwh=V
LENGTH X WIDTH = Base —> full equation could be: Base area x height = volume
Volume of prism (equation)
Vprisim = Base area x height
= B x h
Note: Base AREA used for polygons AND height is defined as the distance between the bases, height is ALWAYS perpendicular to the bases
Height of prism
Height of a prism is the distance between the bases, height is always perpendicular to the bases
Other equations (volume)
Volume/base area = height
Volume/height = base area
Base area x height = volume
Some conversions (Ml=? and gallons = ?)
Ml = cm³
Gallons = by definition are cubed
Prism (definition and equation) also: define “height” of a prism
Definition: A 3-D figure with 2 bases that are congruent and parallel and whose other faces are parallelograms
Equation: Base area x height = Volume AKA: B x h = V
Height: of a prison is the distance between the bases, height it always perpendicular to the bases
Conversion between cubic feet and gallons (and how to convert)
1ft³ = 7.48 gallons
Feet³ = 7.48gal/1 foot —> feet cross cancel and the fraction you multiply it back is equal to one
Intersection
Where shapes cross AKA: when a set of points is in all shapes
Cross section
Intersection of a plane and 3D object/figure
Truncate
Means to cut off
Conic sections
Density (and three equations)
Denser objects have more mass for the same volume
D = m/v
m = d x v
V = m/d
Pyramid and equation for volume
Pyramid: 3D figures with triangular lateral faces and polygon bases
Equation: Vpyramid = 1/3 (Base area x height) = Bh/3
Note: 1/3 because it’s one third of a cube
Ellipse
Another word for oval, can be used for talking about cross sections
Max sides of a cross section
The number of faces
Volume of a cone (equation)
Vcone = (πr² x h)/3
—> contains less volume than may appear, it is one third of a cylinder
Sphere (definition and equation)
Sphere: set of points equidistant from a center point
ratio of Vsphere:Vcylinder = 2:3
Vsphere = 4/3 πr³
Cylinder (volume equation and comparison to sphere)
V = πr²h
Compared: sphere is 2/3 of the volume of a cylinder
Trapezoid AREA formula
A = ((b1 + b2)/2)) (h)
Surface Area of a sphere and why?
Surface area of a sphere = 4πr²
Think about it like a baseball: 4 circles if you lay out the pieces
How to use pyramids to determine the volume of a sphere?
The pyramids’ height is the radius of the sphere.
The sum of the volumes of the pyramids is…
1/3(B1r) + 1/3(B2r) + 1/3(B3r) +….
Factoring we get: 1/3r(B1 + B2 + B3+…)
The sum of all the bases areas is the surface area of the sphere, which has the formula 4πr²
We can substitute this into the “factoring we get:” equation to get a NEW equation: 1/3r(4πr²) = 4/3πr³
This is the volume formula for a hemisphere!!
Vsphere = 4/3πr³
What is a hemisphere (description and volume formula)
3D shape that is half of a sphere.
Vhemisphere = (2/3)πr³
If the edges of a rectangular prism (or any 3D shape) double, how does the surface area change? How does the volume change?
Edges: times n
Area: times n²
Volume: times n³
The top 1/3 of a pyramid has what percent of the total volume? If we dilate a pyramid by a scale factor of 1/3, how does the volume change? (KNOW HOW TO PROVE)
The top 1/3 of a pyramid…
(You can use example numbers)
1/27=4% (around)
—> Why? Plug in a pyramid of 1,1,1 versus 3,3,3
If we dilate a pyramid by 1/3…
Edges: n
Area: n²
Volume: n³