Welcome to Clip from Spiral logo

Interactive video lesson plan for: What are similar triangles? (KristaKingMath)

Activity overview:

You’ve heard about similar triangles, but do you know what technically makes two triangles similar?

Informally, we can say that two triangles are similar if their associated angles are congruent. In other words, their angle measures have to be the same. However, the triangles don’t necessarily have to be the same size, in order for them to still be similar.

The formal definition of similar triangles tells us that two triangles are similar when the associated angles are congruent, and when the associated side lengths are proportional. If both of those conditions are present, then the triangles are similar. If either or both of those conditions are missing, then the triangles are not similar.

0:17 Informal definition of similar triangles // In order for two triangles to be similar, their angles have to the same, but the triangles themselves can still be different sizes.

0:32 Examples of similar triangles //

0:45 Formal definition of similar triangles // In order for two triangles to be similar, their matching angles must be congruent, and the ratio of their matching sides are the same (their sides must be proportional).

2:02 Summary // If two triangles have the same angles and the same side lengths, then they’re congruent (they’re identical). If two triangles have the same angles but different side lengths, then they’re similar. It’s helpful to remember that, just like all squares are rectangles, all congruent triangles are similar triangles.

Music by Joakim Karud: http://soundcloud.com/joakimkarud

● ● ● GET EXTRA HELP ● ● ●

If you could use some extra help with your math class, then check out Krista’s website // http://www.kristakingmath.com


Hi, I’m Krista! I make math courses to keep you from banging your head against the wall. ;)

Math class was always so frustrating for me. I’d go to a class, spend hours on homework, and three days later have an “Ah-ha!” moment about how the problems worked that could have slashed my homework time in half. I’d think, “WHY didn’t my teacher just tell me this in the first place?!”

So I started tutoring to keep other people out of the same aggravating, time-sucking cycle. Since then, I’ve recorded tons of videos and written out cheat-sheet style notes and formula sheets to help every math student—from basic middle school classes to advanced college calculus—figure out what’s going on, understand the important concepts, and pass their classes, once and for all. Interested in getting help? Learn more here: http://www.kristakingmath.com

FACEBOOK // https://www.facebook.com/KristaKingMath/
TWITTER // https://twitter.com/KristaKingMath
INSTAGRAM // https://www.instagram.com/kristakingmath/
PINTEREST // https://www.pinterest.com/KristaKingMath/
GOOGLE+ // https://plus.google.com/+Integralcalc/
QUORA // https://www.quora.com/profile/Krista-King

Tagged under: triangles similar, similar triangles, triangles similar, similar triangles ,geometry, , triangles similar, similar triangles proportional, triangles similar,Krista King, similar triangles,similar triangles, similar triangles, similar triangles,triangle similarity,educational, triangles similar

Clip makes it super easy to turn any public video into a formative assessment activity in your classroom.

Add multiple choice quizzes, questions and browse hundreds of approved, video lesson ideas for Clip

Make YouTube one of your teaching aids - Works perfectly with lesson micro-teaching plans

Play this activity

1. Students enter a simple code

2. You play the video

3. The students comment

4. You review and reflect

* Whiteboard required for teacher-paced activities

Share on:

Share What are similar triangles? (KristaKingMath) on Google+ Share What are similar triangles? (KristaKingMath) on Twitter Share What are similar triangles? (KristaKingMath) on Facebook Pin What are similar triangles? (KristaKingMath) Email What are similar triangles? (KristaKingMath)

Ready to see what else Spiral logo can do?

With four apps, each designed around existing classroom activities, Spiral gives you the power to do formative assessment with anything you teach.


Carry out a quickfire formative assessment to see what the whole class is thinking


Create interactive presentations to spark creativity in class

Team Up

Student teams can create and share collaborative presentations from linked devices


Turn any public video into a live chat with questions and quizzes

1000s of teachers use Spiral to deliver awesome, engaging activities that capture students' understanding during lessons.

Now it's your turn Sign up

Spiral Reviews by Teachers and Digital Learning Coaches

Review of Spiral by teacher: Kathryn Laster @kklaster

Tried out the canvas response option on @SpiralEducation & it's so awesome! Add text or drawings AND annotate an image! #R10tech

Review of Spiral by teacher: Room 220 Math Stars @3rdgradeBCE

Using @SpiralEducation in class for math review. Student approved! Thumbs up! Thanks.

Review of Spiral by teacher: Miss Ord @ordmiss

Absolutely amazing collaboration from year 10 today. 100% engagement and constant smiles from all #lovetsla #spiral

Review of Spiral by teacher: Adam J. Stryker @strykerstennis

Students show better Interpersonal Writing skills than Speaking via @SpiralEducation Great #data #langchat folks!

Review of Spiral by teacher: Dr Ayla Göl @iladylayla

A good tool for supporting active #learning.

Review of Spiral by teacher: Brett Erenberg @BrettErenberg

The Team Up app is unlike anything I have ever seen. You left NOTHING out! So impressed!

Get the Clip Chrome Extension & Create Video Lessons in Seconds

Add Clip to Chrome