It’s important to understand the different symbols that are associated with geometry, so that when you’re asked a question, you know what you’re being asked, and you also know how to answer.
In this video, we’re going to talk about the different symbols that are associated with angles, specifically.
Next lesson: Area and Perimeter of a Triangle[divider]The following transcript is provided for your convenience.[divider]
So, here we have two triangles, triangle ABC and triangle DEF.
We’re going to answer the following three questions, and we’ll talk about what the symbols mean as we go.
The first one is, name the angles in triangle ABC. There are a couple of different ways to name angles.
One way is to use angle symbol (∠), and just the letter of the vertex of the angle. So, we would call this angle, ∠A, since A is the vertex. This angle would be called ∠B, so we use the angle symbol, and the letter for the vertex. The last angle would be ∠C. Again, this is the angle symbol, and you name it by its vertex.
The other way to name angles would be to use the three letters for the angle. So, ∠A could be called ∠BAC. Notice that the vertex is in the center of the name, and we still use that angle symbol to name it. It looks very similar to the less than sign (<), but the bottom is straight. To name ∠B, we could also name it ∠ABC, or ∠CBA, as long as that B stays in the middle. And then ∠C can be called ∠BCA, or ∠ACB, again, that vertex needs to be the middle letter. So, we start with our angle symbol, ∠ACB.
So, there are two different ways to name angles, all using the angle symbol.
Next, we need to name the congruent angles in triangle ABC and triangle DEF. Congruent means the same or equal, the same, and congruent angles are marked for you sometimes on pictures, and the way you’ll know which angles are congruent is because they’ll be marked in the same way.
So, since ∠A and ∠D have the same mark on them, that means that ∠A ≅ ∠D. We use our angle symbols again, and this time, in the middle, means congruent. It’s an equal sign with a little squiggly on top. ∠B is marked similarly to ∠E, and we’re going to talk about this symbol in just a minute, ∠B ≅ ∠E. Finally, ∠C and ∠F are marked the same way, they both have these two marks on the angle, so that means that they’re congruent to each other, ∠C ≅ ∠F.
Now, this last questions says, what is the m∠B? This m stands for measure, and so when you see the m, that means they want the degree. How many degrees are in the angle? What’s the measure of the angle? ∠B, even though there isn’t a number there, this box means that ∠B measures to be 90°. So, the m∠B = 90, and the m∠E would also be 90°.
Next lesson: Area and Perimeter of a Triangle