Classifying shapes by line and angles types
About this video
This video finds the side perpendicular to side BC by looking for the right-angle symbol, then sorts triangles into right, obtuse and acute groups. A right triangle has a 90-degree angle, an obtuse triangle has an angle over 90 degrees, and an acute triangle has all three angles under 90 degrees.
You'll be able to
- find perpendicular sides using the right-angle symbol.
- sort triangles into right, obtuse and acute triangles.
Key words
- perpendicular
- Meeting at a right angle (90 degrees).
- right triangle
- A triangle with one 90-degree angle.
- obtuse triangle
- A triangle with one angle larger than 90 degrees.
- acute triangle
- A triangle where all three angles are less than 90 degrees.
Transcript
Which side is perpendicular to side BC? So BC is this line segment right over here. And for another segment to be perpendicular to it, perpendicular just means that the two segments need to intersect at a right angle, or at a 90-degree angle. And we see that BC intersects AB at a 90-degree angle.
This symbol right over here represents a 90-degree, or a right angle. So we just have to find side AB or BA. And that's right over here. Side AB is perpendicular to side BC. Let's do a few more of these. Put the triangles into the correct categories, so this right over here.
So let's see. Let's think about our categories. Right triangles-- so that means it has a 90-degree angle in it. Obtuse triangles-- that means it has an angle larger than 90 degrees in it. Acute triangles-- that means all three angles are less than 90 degrees. So this one has a 90-degree angle.
It has a right angle right over here. So this is a right triangle. This one right over here, all of these angles are less than 90 degrees, just eyeballing it. So this is going to be an acute-- that's going to be an acute triangle. I'll put it under acute triangles right over there.
Then this one over here, this angle up here, this is-- and we can assume that these actually are drawn to scale, this is more open than a 90-degree angle. This is an obtuse angle right over here. It's going to be more than 90 degrees. So this is an obtuse triangle.
Now, this one over here, all of them seem acute. None of them even seem to be a right angle. So I would put this again into acute-- acute triangles. This one here clearly has a right angle. It's labeled as such. So we'll throw it right over here. And then this one, this angle right over here is clearly even larger.
It has a larger measure than a right angle. So this angle right over here is more than 90 degrees. It's going to be an obtuse angle. So we will throw it into obtuse-- obtuse triangles. So we got two in each of these. And let's check our answer. We got it right.
Video © Khan Academy, used under CC BY-NC-SA. Watch on Khan Academy. Puzzicle is not affiliated with Khan Academy.