Rotating a Triangle 90 Degrees

Oct 13, 2025 by wbrum.org 2 views

Introduction

In geometry, transformations are essential concepts that help us understand how shapes change under various operations. One common transformation is rotation, where a shape is rotated by a certain angle around a fixed point, known as the origin. In this article, we will explore the transformation rule that describes a triangle rotated 90 degrees about the origin.

Understanding Rotation

Rotation is a transformation that turns a shape around a fixed point, called the origin. The origin is typically represented as the point (0, 0) on the coordinate plane. When a shape is rotated, its position changes, but its size and shape remain the same.

Rotating a Triangle 90 Degrees

To rotate a triangle 90 degrees about the origin, we need to understand how the coordinates of the triangle's vertices change. Let's consider a triangle with vertices at (x, y), (a, b), and (c, d). When we rotate this triangle 90 degrees about the origin, the new coordinates of the vertices are:

(x, y) → (-y, x)
(a, b) → (-b, a)
(c, d) → (-d, c)

Analyzing the Transformation Rule

Now, let's analyze the transformation rule that describes the rotation of the triangle. We can see that the x-coordinate of each vertex is replaced by the negative of its y-coordinate, and the y-coordinate is replaced by the negative of its x-coordinate. This is a classic example of a 90-degree rotation about the origin.

Comparing the Options

Let's compare the transformation rule we derived with the options provided:

A. (x, y) → (-x, -y) - This option describes a reflection across the origin, not a rotation.
B. (x, y) → (-y, x) - This option matches the transformation rule we derived.
C. (x, y) → (-y, -x) - This option describes a rotation of 180 degrees about the origin, not 90 degrees.

Conclusion

In conclusion, the transformation rule that describes a triangle rotated 90 degrees about the origin is (x, y) → (-y, x). This rule indicates that the x-coordinate of each vertex is replaced by the negative of its y-coordinate, and the y-coordinate is replaced by the negative of its x-coordinate.

Key Takeaways

Rotation is a transformation that turns a shape around a fixed point, called the origin.
The transformation rule for rotating a triangle 90 degrees about the origin is (x, y) → (-y, x).
This rule indicates that the x-coordinate of each vertex is replaced by the negative of its y-coordinate, and the y-coordinate is replaced by the negative of its x-coordinate.

Further Exploration

Explore other types of transformations, such as reflection and translation.
Practice rotating shapes using different angles and coordinates.
Apply transformation rules to solve problems in geometry and trigonometry.

Glossary of Terms

Origin: The fixed point around which a shape is rotated.
Rotation: A transformation that turns a shape around a fixed point.
Transformation rule: A mathematical expression that describes how a shape changes under a transformation.

References

[1] Geometry textbook by [Author's Name]
[2] Online resources for geometry and trigonometry

Additional Resources

Online geometry and trigonometry courses
Geometry and trigonometry practice problems
Math software and apps for visualizing transformations
A Triangle Rotated 90 Degrees About the Origin: Q&A =====================================================

Introduction

In our previous article, we explored the transformation rule that describes a triangle rotated 90 degrees about the origin. In this article, we will answer some frequently asked questions about this topic.

Q: What is the difference between a rotation and a reflection?

A: A rotation is a transformation that turns a shape around a fixed point, called the origin. A reflection, on the other hand, is a transformation that flips a shape across a line or a point. For example, a rotation of 90 degrees about the origin is different from a reflection across the x-axis.

Q: How do I determine the transformation rule for a rotation?

A: To determine the transformation rule for a rotation, you need to understand how the coordinates of the shape's vertices change. For a 90-degree rotation about the origin, the new coordinates of the vertices are:

(x, y) → (-y, x)
(a, b) → (-b, a)
(c, d) → (-d, c)

Q: What is the transformation rule for a 180-degree rotation about the origin?

A: The transformation rule for a 180-degree rotation about the origin is (x, y) → (-x, -y). This rule indicates that the x-coordinate of each vertex is replaced by the negative of its x-coordinate, and the y-coordinate is replaced by the negative of its y-coordinate.

Q: Can I rotate a shape by an angle other than 90 or 180 degrees?

A: Yes, you can rotate a shape by any angle. However, the transformation rule will be more complex and may involve trigonometric functions.

Q: How do I apply the transformation rule to a shape?

A: To apply the transformation rule to a shape, you need to substitute the coordinates of the shape's vertices into the transformation rule. For example, if you have a triangle with vertices at (x, y), (a, b), and (c, d), and you want to rotate it 90 degrees about the origin, you would substitute the coordinates into the transformation rule:

(x, y) → (-y, x)
(a, b) → (-b, a)
(c, d) → (-d, c)

Q: What are some real-world applications of rotation?

A: Rotation has many real-world applications, including:

Designing and building structures, such as bridges and buildings
Creating art and graphics
Understanding the motion of objects in physics and engineering
Solving problems in computer science and data analysis

Q: Can I use technology to help me with rotation?

A: Yes, you can use technology to help you with rotation. There are many math software and apps that can visualize and perform rotations, making it easier to understand and apply the transformation rule.

Q: What are some common mistakes to avoid when working with rotation?

A: Some common mistakes to avoid when working with rotation include:

Confusing rotation with reflection
Not understanding the transformation rule
Not applying the transformation rule correctly
Not checking the results for accuracy