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### Course: Geometry (FL B.E.S.T.)>Unit 3

Lesson 1: Rigid transformations overview

# Getting ready for transformation properties

Finding missing triangle angle measures, area and perimeter, and angle measures on transversals help prepare us to learn the properties of transformations.
Let's refresh some of the earlier concepts that will come in handy as we dig deeper into transformations. Then we'll look ahead to how the idea will help us with transformation properties.

## Finding missing angle measures in triangles

### Practice

Problem 1
Find the value of $x$ in the triangle shown below.
$x=$
$\mathrm{°}$

For more practice, go to Find angles in triangles.

### Where will we use this?

When we can transform one figure onto another using only rigid transformations, the two figures are congruent. We'll use congruence along with other concepts, like the fact that the interior angle measures of a triangle sum to $180\mathrm{°}$, to find missing measurements.
We'll use this skill in the Find measures using rigid transformations exercise.

## Finding area and perimeter

### Practice

Problem 2.1
What is the area of the rectangle?
square centimeters

### Where will we use this?

Rigid transformations preserve length, so we can use the measurements in a congruent figure to help us calculate the perimeter or area of another figure.
We'll use these skills in the Find measures using rigid transformations exercise.

## Using angle measures from transversals

### Practice

Problem 3
Below are two parallel lines with a third line intersecting them.
Label each angle with its angle measure.
You may use each label as many or as few times as you need.
Click each dot on the image to select an answer.

For more practice, go to Angle relationships with parallel lines.

### Where will we use this?

Rigid transformations preserve angle measure. The properties of angle measures on transversals will help us make sense of why translations and dilations take lines to parallel lines, but rotations and reflections usually don't.
Here are a couple of the exercises that build off of angle measures with transversals:

## Want to join the conversation?

• why do we need this in real life
• cuz our teachers tell us too
• is it normal for my school to go Algebra 1, Geometry, then Algebra 2.
• Yeah my school does that
• I'm extremely confused on problem 2.2 on finding the area of the triangle. It looks off and I got a total different answer which is 14 1/2. :(
• For a triangle, the area is 1/2 bh. You always want the base and the height to be perpendicular to each other, so the base is 2 and the height is 5. You should never use a side that is at any angle that is not 90 degrees.
• Guys something i learned recently that helps A LOT is basically yk how when rotating clockwise is negative and counterclockwise is positive, well if you are able to, just turn your screen. So say its positive 90 degrees, you flop your computer or tablet on its side and picture the numbers being in the right place. It basically shows you what its supposed to look like once it is already rotated. I hope this helps!!
• What are rigid transformations? And how do they work? what do we use them for irl?
• Rigid transformations are transformations where angles and lengths of shapes are preserved. It is like taking the same exact shape or object and moving it by reflecting it or rotating it. We use rigid transformations everyday simply by picking up and placing items somewhere else. (Like if you were to pick up a pencil and move it beside you).
• This is hard for me, at least the angles and triangle area type deal. I did these in advanced 7th grade and we went so fast I didn't even have time to memorize it. Think i failed that unit too. :/ Yeah this is a little bit of a struggle.
• I do not quite understand this from the article, "The properties of angle measures on transversals will help us make sense of why translations and dilations take lines to parallel lines, but rotations and reflections usually don't."