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 3
A cuboid is shown below:
What is the surface area of the cuboid?
Incorrect
Correct Answer:
62
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
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 #2
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:
height*length*width
We replace the data in the formula:
3*5*7
7*5 = 35
35*3 = 105
Answer
105 cm³
Exercise #3
A cuboid has a length of is 9 cm.
It is 4 cm wide and 5 cm high.
Calculate the volume of the cube.
Video Solution
Step-by-Step Solution
To solve this problem, we'll follow these steps:
Step 1: Identify the given dimensions: length = 9 cm, width = 4 cm, height = 5 cm.
Step 2: Apply the formula for the volume of a cuboid, V=length×width×height.
Step 3: Calculate the value by substituting the given dimensions into the formula.
Now, let's work through each step:
Step 1: Given dimensions are:
- Length = 9 cm
- Width = 4 cm
- Height = 5 cm
Step 2: Use the formula for the volume of a cuboid: V=length×width×height
Step 3: Substitute the values into the formula: V=9cm×4cm×5cm
Calculate the product: V=180cm3
Therefore, the volume of the cuboid is 180cm3.
Answer
180 cm³
Exercise #4
Shown below is a cuboid with a length of 8 cm.
Its width is 2 cm and its height is 4 cm.
Calculate the volume of the cube.
Video Solution
Step-by-Step Solution
To solve this problem, we'll follow these steps:
Step 1: Identify the given dimensions of the cuboid.
Step 2: Apply the formula for the volume of a cuboid.
Step 3: Perform the calculation using the known dimensions.
Now, let's work through each step:
Step 1: The problem states that the cuboid has a length of 8 cm, a width of 2 cm, and a height of 4 cm.
Step 2: We will use the volume formula for a cuboid, which is:
V=length×width×height
Step 3: Substituting the given dimensions into the formula, we have:
V=8cm×2cm×4cm
Performing the multiplication:
V=16cm2×4cm=64cm3
Therefore, the volume of the cuboid is 64cm3.
Answer
64 cm³
Exercise #5
A cuboid is 9 cm long, 4 cm wide, and 5 cm high.
Calculate the volume of the cube.
Video Solution
Step-by-Step Solution
To calculate the volume of the cuboid, we apply the formula for the volume of a cuboid:
V=length×width×height
Given:
Length = 9 cm
Width = 4 cm
Height = 5 cm
Now, substituting the values into the formula:
V=9×4×5
First, multiply 9 and 4:
9×4=36
Then, multiply the result by 5:
36×5=180
Therefore, the volume of the cuboid is 180 cm³.
Since this is a multiple-choice question, the correct choice is 4: 180 cm3.