# Constructing angles | Geometry | 4th grade | Khan Academy

We’re asked to construct

a 10 degree angle. So we have this

little angle tool here that we can use

to construct an angle. So just like that. And then they give

us a protractor to actually measure the angle. So let’s set it up. Let’s put the protractor here. Let’s put the

vertex of the angle at the center of the protractor,

in other words, center the protractor at the

center of the vertex. Looks like the protractor’s

a little bit easier to manipulate. So let’s do that there. Now let’s put one of the

rays here at 0 degrees. And now I’m going to put

the other ray at 10 degrees. And it looks like I am done. I have constructed

a 10 degree angle. And you want to be

careful here when you use this tool because

the angle in question– let me move the protractor show

you what I’m talking about– that this right over here is the

angle that we’re talking about. If I’d switched these two rays,

the way the tool is set up, it might have

interpreted the angle as this outer angle

right over here. So be careful to look at which

angle we’re actually measuring. But this looks like I

did the 10 degree angle. So let me check my answer. And just to be clear

what I’m talking about. If you did the 10

degree angle like this, then it definitely would

have marked it wrong even though the interior angle

right over here or this angle right here might be 10 degrees. The way the tool is set up,

you see from this circle, that it thinks that you’re

looking at this outer angle. So it’s important to

make sure, at least for the sake of this

exercise, that the system, that the computer

program knows which angle you’re going

to talk about. Let’s do one more of these. 155 degree angle. And this one’s

interesting because this is an obtuse angle. So once again, let

us put the protractor at the vertex of the angle. So just like that. And now that seems pretty good. Now let’s take one ray

and put it at 0 degrees, and then let’s take the

other one and put it at 155. So once again, 10, 20,

30, 40, 50, 60, 70, 80, 90– that gets us

to a right angle. Then we’ll start getting into

obtuse angles, 100, 110, 120, 130, 140, 150. And just to make

sure that blue arc is measuring this angle right

over here, not the outer one. And let me move the

protractor out of the way so we can get a good look at it. And we got it wrong. So let’s see what we–

oh, 155 degree angle, not 150 degree angle. Let me fix that. 155 degree angle. Now we got it right.

No Comments! WHA?!

Be sure to look at the questions, Sal! Your videos are super helpful but this was the first time I saw u make a mistake!

ya

no but i don't get it where did he get it wrong?

what's the name of the app?😊

thanks for the vid for my homework

Helpful

it is dome

Happy Ramadan everyone!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!