So far we have worked with common two-dimensional figures such as the square or the triangle. Three-dimensional figures are those that extend into the third dimension, meaning that in addition to length and width, they also have height (that is, the figure has depth).
What differences do three-dimensional figures have?
Three-dimensional figures have several definitions that we will see next: Below is a three-dimensional figure that we will use to learn each definition - The cube:
Face: it is the flat side of a three-dimensional figure In the cube we have here, there are 6 faces (one of them is painted gray) Edge: these are the lines that connect one face to another in a three-dimensional figure In the cube we have here, there are 12 edges (painted green) Vertex: it is the point that connects the edges In the cube we have here, there are 8 vertices (painted orange)
Volume: it is the amount of space contained within a three-dimensional figure. The units of measurement are cm3 .
The cuboid is a three-dimensional figure composed of 6 rectangles.
Each cuboid has:
6 faces: the rectangles that make up the cuboid - three pairs of rectangles that can be different from each other. 12 edges: the edges of the cuboid (divided into length, width, and height) - marked in green 8 vertices: the points where the edges meet - marked in orange
It is the sum of the area of the four lateral rectangles (without the bases). The lateral area of a cuboid can be calculated with the following formula: a- Length b- Width h- Height
The cylinder is a three-dimensional figure composed of two identical parallel circles called bases, between which the lateral area expands.
Other properties:
The distance between the two bases is constant and is called the height of the cylinder - we will mark it with an H The radius of both bases is equal, we will mark it with an R
Volume of the cylinder
The volume contained within the cylinder is usually denoted by V. Formula to calculate the volume of the cylinder: π×R2×=˝V
When:
π = PI (3.14) R = Radius of the base H = Height of the cylinder
Let's practice! In a right triangular prism, are the triangular bases always identical? Solution: Yes! The triangles, which are actually the bases, are always the same. Exercise: How many heights are there in a right triangular prism? Are they identical? Solution: There are 3 heights in a right triangular prism and they always have the same length. Exercise: Do the three rectangles that make up the lateral faces of the prism have to be identical? Solution: No. The edges of the triangle do not necessarily have to be equal and this could create different rectangles.
Volume of the right triangular prism
The volume of the prism is usually expressed through the following formula: V=S⋅H
Identify the correct 2D pattern of the given cuboid:
Incorrect
Correct Answer:
Question 2
An orthohedron has the dimensions: 4, 7, 10.
How many rectangles is it formed of and what are their dimensions?
Incorrect
Correct Answer:
2 Rectangles 4X7
2 Rectangles 4X10
2 Rectangles 7X10
Question 3
Look at the cuboid below:
What is the volume of the cuboid?
Incorrect
Correct Answer:
480 cm³
Area of a right triangular prism
The area of a right triangular prism is, in fact, the total sum of the surfaces of its two bases (the triangles) and its three lateral faces (the rectangles).
Examples and exercises with solutions of three-dimensional figures
Exercise #1
Look at the cuboid below:
What is the volume of the cuboid?
Video Solution
Step-by-Step Solution
To determine the volume of a cuboid, we apply the formula:
Step 1: Identify the dimensions of the cuboid:
Length (l) = 12 cm
Width (w) = 8 cm
Height (h) = 5 cm
Step 2: Apply the volume formula for a cuboid:
The formula to find the volume (V) of a cuboid is:
V=l×w×h
Step 3: Substitute the given dimensions into the formula and calculate:
V=12×8×5
Step 4: Perform the multiplication in stages for clarity:
First, calculate 12×8=96
Then multiply the result by 5: 96×5=480
Therefore, the volume of the cuboid is 480cm3.
Answer
480 cm³
Exercise #2
Look at the cuboid below.
What is the surface area of the cuboid?
Video Solution
Step-by-Step Solution
Let's see what rectangles we have:
8*5
8*12
5*12
Let's review the formula for the surface area of a rectangular prism:
(length X width + length X height + width X height) * 2
Now let's substitute all this into the exercise:
(8*5+12*8+12*5)*2= (40+96+60)*2= 196*2= 392
This is the solution!
Answer
392 cm²
Exercise #3
A cuboid is shown below:
What is the surface area of the cuboid?
Video Solution
Step-by-Step Solution
Remember that the formula for the surface area of a cuboid is:
(length X width + length X height + width X height) 2
We input the known data into the formula:
2*(3*2+2*5+3*5)
2*(6+10+15)
2*31 = 62
Answer
62
Exercise #4
Given the cuboid of the figure:
What is its volume?
Video Solution
Step-by-Step Solution
To solve this problem, we'll calculate the volume of the cuboid using the given dimensions:
Step 1: Identify the dimensions
Step 2: Apply the volume formula for a cuboid
Step 3: Calculate the volume
Let's work through these steps:
Step 1: From the diagram, we are informed of two dimensions directly: the width w=5 and the height h=4. The diagram also indicates the horizontal length (along the base) is l=9.
Step 2: To find the volume of the cuboid, we use the formula: Volume=length×width×height.
Step 3: Substituting the identified dimensions into the formula, we have: Volume=9×5×4.
Calculating this, we find: 9×5=45, 45×4=180.
Therefore, the volume of the cuboid is 180 cubic units.
This corresponds to choice \#4: 180.
Answer
180
Exercise #5
Calculate the volume of the cuboid
If its length is equal to 7 cm:
Its width is equal to 3 cm:
Its height is equal to 5 cm:
Video Solution
Step-by-Step Solution
The formula to calculate the volume of a cuboid is: