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Course: Geometry (SCPS pilot: textbook aligned) > Unit 4
Lesson 1: Congruence and transformations- Rigid transformations intro
- Dilations intro
- Translations intro
- Rotations intro
- Identifying transformations
- Identify transformations
- Getting ready for congruence
- Congruent shapes & transformations
- Non-congruent shapes & transformations
- Congruence & transformations
- Segment congruence equivalent to having same length
- Angle congruence equivalent to having same measure
- Properties of congruence and equality
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Getting ready for congruence
Finding missing triangle angle measures and identifying parallel lines from angle measures on transversals help prepare us to learn about congruence.
Let’s refresh some concepts that will come in handy as you start the congruence unit of the high school geometry course. You’ll see a summary of each concept, along with a sample item, links for more practice, and some info about why you will need the concept for the unit ahead.
This article only includes concepts from earlier courses. There are also concepts within this high school geometry course that are important to understanding congruence. If you have not yet mastered the Intro to Euclidean geometry lesson, the Rigid transformations overview lesson, or the Properties & definitions of transformations lesson, it may be helpful for you to review those before going farther into the unit ahead.
Using angle relationships
What is this, and why do we need it?
When lines intersect, especially when a transversal intersects a pair of parallel lines, the intersections form angles with special relationships. We will use these angle relationships to explain how to construct parallel or perpendicular lines, which in turn help us to bisect angles and line segments. We will also use parallel sides to reveal more properties of parallelograms.
Practice
For more practice, go to Angle relationships with parallel lines.
Where will we use this?
Here are a few of the exercises where reviewing angle relationships might be helpful:
Finding missing angle measures in triangles
What is this, and why do we need it?
The three angle measures in any triangle add up to . We'll use congruence along with other concepts, like the fact that the interior angle measures of a triangle sum to , to find missing measurements.
Practice
For more practice, go to Find angles in triangles.
Where will we use this?
Here are the first few exercises where reviewing angle measures in triangles might be helpful.
Want to join the conversation?
- For the first practice question,how do we know that line a and line d have alternate interior angles and corresponding angles,and why does it not work for line b and line c?(25 votes)
- Any pair of lines have these angles, so the question is are they congruent (if you use alternate interior or alternate exterior or corresponding)?
or are they supplementary (if you use same side interior or same side exterior)?
For any one line and the transversal, you can use the fact that adjacent angle are supplementary and vertical angles are congruent.
Thus, for b and c, alternate interior angles would be 88 degrees (180-92) and 91 degrees which are not congruent, thus not parallel. For corresponding angles, you would get the same results of 88 and 91 degrees which are not congruent.(15 votes)
- what exactly does congruence mean?(5 votes)
- congruence is to figures as equal is to expressions. If two things are congruent, they are the same size and/or the same shape.(15 votes)
- As a freshman who started high school yesterday, I am really going to need this as I am in an honors course(10 votes)
- How do you know which one is parallel and which one is not?(1 vote)
- If you fine two congruent angles, you know it is parallel. Also, you can use a compass. If you're still confused, the next few videos shall help.
-Duskpin the Avatar(6 votes)
- I am still confused as to how a and d were parallel. line d was 89 degrees and line a was 91.(3 votes)
- the angles add up to 180 degrees and so it makes them parallel. hope that helps.(5 votes)
- What is this questions about(3 votes)
- things for the future.(3 votes)
- I have a hard time doing geometry. do you have any tips on how to get better?(4 votes)
- Practice! If you feel like you are running out of practice, search worksheets up on google, and watch videos. Trust me, it really makes math a lot easier :)(1 vote)
- i am a little confused here. what is congruence exactly??(2 votes)
- Congruence compares two line segments, shapes, or 2-d figures. It two things are exactly the same shape and same size, then they are congruent. If two line segments are congruent, that would mean their lengths would be the same. If two figures are congruent (like congruent triangles), then their angles are the same and their side lengths are the same.(4 votes)
- What is the exact definition of congruence?(3 votes)
- I think its something like this:
2 Shapes that has all of its edges equal, (interior and exterior) angles equal. To obtain one shape from another, you can rotate it definite times, translate it definite times, but cannot reflect it, nor dilate or expand it.
https://byjus.com/maths/congruence-of-triangles/(2 votes)
- I don't get this. could i get help?(4 votes)
- Congruence means that the shapes are equal in all ways which also means that with a set of rigid transformations you can map one onto the other.(0 votes)