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### Course: Geometry (FL B.E.S.T.) > Unit 9

Lesson 6: Volume and surface area# Volume formulas review

Review the formulas for the volume of prisms, cylinders, pyramids, cones, and spheres.

It may seem at first like there are lots of volume formulas, but many of the formulas share a common structure.

## Prisms and prism-like figures

We always measure the height of a prism perpendicularly to the plane of its base. That's true even when a prism is on its side or when it tilts (an oblique prism).

### Rectangular prisms

Often, we first learn about volume using rectangular prisms (specifically right rectangular prisms), such as by building the prism out of cubes.

Note that any face of a rectangular prism could be its base, as long as we measure the height of the prism perpendicularly to that face.

### Triangular prisms

A triangular prism has a base shaped like a triangle.

### Cylinders

A circular cylinder is a prism-like figure that has a base shaped like a circle.

### Oblique prisms

In oblique prisms, the bases are in parallel planes,

We still calculate the volume in exactly the same way because of Cavalieri's principle.

## Pyramids and pyramid-like figures

We also measure the height of a pyramid perpendicularly to the plane of its base. Because of Cavalieri's principle, the same volume formula works for right and oblique pyramid-like figures.

### Rectangle-based pyramids

A rectangle-based pyramid has a base shaped like a rectangle.

### Cones

A circular cone is a pyramid-like figure that has a base shaped like a circle.

### Spheres

## Want to join the conversation?

- Why is the Volume of sphere is divided by 3?(16 votes)
- This is a really good video that I found:

https://www.youtube.com/watch?v=xuPl_8o_j7k

It explains the formula with simple geometry and algebra, and in animation.(26 votes)

- if a square is writen X^2 how is a cube writen(0 votes)
- A number cubed, or in this case x, is written as x³, or x^3.(59 votes)

- who found the proof to the volume of sphere? better question, how?(9 votes)
- Click on the line of text under the section "Volume of a Sphere" that reads: "Where does this formula come from?" It gives a, in my opinion, somewhat ambiguous answer, but it is an answer nonetheless.(4 votes)

- When using the pi symbol in calculations, the answer comes out differently than if you just use 3.14, which is how the answers on here are calculated. Why not just recommended to use only 3.14 for pi, not the symbol on calculators as shown on the videos? It is frustrating to get sent back to zero when you use your calculator correctly but you should just use one standard calculation of 3.14.(5 votes)
- 3.14 is a simplified version of the real value of pi:

3.141592653589793238462643383279502884197169399375105820974944592307816406286

http://www.geom.uiuc.edu/~huberty/math5337/groupe/digits.html(11 votes)

- Will all the volume formulas be available on the math sheet at the SAT?(10 votes)
- They provide it for you.(1 vote)

- how can I find volume of a tetrahedron(4 votes)
- A tetrahedron is just a triangular pyramid. If any pyramid has height h and a base of area b, then it's volume is bh/3.(6 votes)

- What would be the equation to find the volume for a trapezoid prism?(0 votes)
- Any prism volume is V = BH where B is area of base and H is height of prism, so find area of the base by B = 1/2 h(b1+b2), then multiply by the height of the prism.(14 votes)

- What would be the difference between a triangular prism and a pyramid?(3 votes)
- A prism has the base that goes through the whole figure, so a triangular prism will have two congruent bases that are a triangle. A triangular pyramid has a triangular base and each base vertex that has an edge that goes to a common vertex.(6 votes)

- 01101001 00100000 01101100 01101111 01110110 01100101 00100000 01101101 01100001 01111000 00100000 01110000 01100101 01110100 01100101 01110010(4 votes)
- 01010111 01101000 01101111 00100111 01110011 00100000 01110100 01101000 01100001 01110100 00111111(3 votes)

- When we need to use the value of pi to find the area of a circle for part of the problem, which number value of pi would be better to use to find a more exact calculation? Would it be 3.14, the symbol for pi, or 22/7?(3 votes)
- pi = 3.14156...

3.14

22/7 = 3.1428...

So 3.14 will give a slightly underestimate it, and 22/7 will slightly overestimate it. The 15 in the thousands/ten thousands place is only slighty closer to 22/7 than to the 00 of 3.14, so it may give only slightly closer answer than using π. If the problem states what they want you to use, then you have to use that. Most calculators have a π button which will give you the closest answer once you round.(5 votes)