Vertex Angle of an Isosceles Triangle

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Vertex Angles of a Kite: Lesson for Kids

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:02 Real-Life Triangles
  • 0:26 Isosceles Triangles
  • 0:53 The Vertex Angle
  • 1:25 Measuring the Vertex Angle
  • 2:37 Practice Problem
  • 3:35 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Timeline
Autoplay
Autoplay
Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Mark Boster
You probably know what an angle is, but what is a vertex? Or for that matter, what is an isosceles triangle? And where is the vertex angle in an isosceles triangle? Don't know? That's okay. You are about to find out.

Real-Life Triangles

Tony and Pat made a shirt for their mother. It was beautiful. However, when Mom tried it on, the left sleeve went to her elbow, and the right sleeve went to her wrist. They tried again, but this time, the left sleeve was longer than the right sleeve. What to do? If Tony and Pat had remembered what they'd learned about isosceles triangles, this problem could have been solved.

Isosceles Triangles

Isosceles triangles are triangles that have two legs, or sides, of the same length. The third side of the triangle can either be longer or shorter than the other two. An easy way some people have found to remember the word isosceles is to say it or think of it as 'I saw some sleeves.' Say it fast and it sort of sounds like isosceles, huh?

Well, anyway, shirts have two sleeves. Both sleeves are the same length. So, I saw some sleeves!

The Vertex Angle

Isosceles: I Saw Some Sleeves
null

There is a triangle drawn over this person in a lime green shirt. Yes, it's an isosceles triangle. It has two sides of the same length, like sleeves, and one of another length. The two equal sides of the isosceles triangle are also called legs. The third side of the isosceles triangle, the side not the same length as the other two, is called the base. Across from the base is the vertex angle, the angle formed by the two sides of the same length. In the diagram, the person's head is at the vertex of this isosceles triangle.

Measuring the Vertex Angle

There are two ways that you can find the measurement of the vertex angle. As you may already know, the angles in all triangles total 180°. Let's take an isosceles triangle where each base angle is 75°. Since 75° + 75° = 150°, 150° of the triangle are accounted for. Since 180° - 150° = 30°, the vertex angle must be 30° so that the angles of the triangle total 180°.

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account
Support