Review of lines and angles - Lines & Angles Video Lecture - Class 7

ok so let us quickly review on the few
basic topics that we covered in earlier
grades so let's just first start with
what do we mean by a line segment so we
know that a line segment has two
endpoints the figure number one here
shows a line segment and we have this
point B and Q right so line segments
simply is characterized by a line having
two end points right and we denote this
line as PQ right or you can even just
write this or simply you can say BQ
that's this the line segment PQ then let
us look at line line is nothing but the
concept of line segments extended
further so in line segments there are no
end point so if you see that we have
these two points and they are two points
and they are extending here this this
line is extending infinitely in both the
directions and this is what the arrows
represent so that is what is a line
segment and array is nothing but a line
segment or a line which has one endpoint
so in this case we have this row a raid
0 P and we represent array as opie
followed by a single arrow so just shows
array and if I want to represent the
line a be really present a be as this
showing the air on both the sides which
shows that the line this is a line
extending indefinitely in both the
directions we also use a letter L mm to
represent line so we can say this is a
line L or a line m online n just for the
sake of simplicity instead of writing
this notation every time it is easier
for us to use a single letter ok so that
was about lying ray and line segment now
let us quickly review water angles now
if you remember angles are nothing but
the corners and the corners are formed
whenever two line segments or two lines
meet so for example if
look at this figure here which is that
of a triangle and what do we see is we
have three angles over here and how do
we say that we have three angles because
this segment and this segment they meet
over here they meet at this point right
so this we known as vertex if you
remember so wherever there is a vertex
there is an angle similarly this segment
and this segment right they are meeting
at this point or this vertex and we have
angled so let's say this is an angle a
oh let's say this is an angle a let's at
this angle B and this angle C so we have
three angles over here right now
similarly if you look at this we have
just two simple line segments okay and
they are meeting at this point and we
can you can see that it is forming
angles this is one angle this is another
angle let me write this angle one angle
to angle three and angle for so simply
angles are formed whenever we have two
lines meeting at a point okay now let us
recollect some basic types of angles so
we learn that there is an acute angle
and an Acura angle is an angle which is
between 0 to 90 degrees now if you
remember acute angle could be something
like let's say that we have this and
something like this so this is an acute
angle we could even draw another angle
here or we could draw this ray over here
or here or here or we can keep on doing
all the way long till you reach 90
degree the moment we have a 90 degree
angle we call it as a right angle right
angle is an angle which is equal to 90
degrees as is shown over here right and
any angle that is less than 90 degrees
that is still here till here right we
can say that that angle
is an acute angle okay then we come to
an obtuse angle an obtuse angle is
between 90 to 180 degrees that is when
we start looking at the other part of
the angle if you see here when we extend
it beyond 90 degrees so the same ray I
am drawing different angles if you can
see that right so if I were to look at
it in another way what we can do is
something like this so we make a
straight line and then we make an angle
like this perpendicular right and if I
want to now say which angles are which
we can say that from here to here any
angle that lies from here is an acute
angle this angle which is like 90
degrees right this is a right angle and
any angle that lies in this area that is
an obtuse angle right so because this is
90 degrees this is 0 to 90 degrees and
this is 90 to 180 degrees right so and
that is an obtuse angle so these were
some of the basic ideas of angles and
lines now in the next session we'll
start looking at more details about
different types of related angles