Examples with perpendicular lines and right, obtuse, acute triangles

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.