L11 : Questions 1: RHS - Congruence of Triangles , Maths, Class 7 Video Lecture

hello friends this video on congruence
of triangles path 11 is brought to you
by exam for calm no more fear from exam
so based on whatever we have learned in
our HS criteria let us again quickly try
to attempt a few questions which
confluence criteria do you use in the
following so here it says that Z X is
equal to RT so said X is equal to RT so
this side is equal and Q is equal to Z
minus so R cube that as this side is
equal to Z Y which is this side angle p
RQ angle t R Q this angle is equal to
angle XZ viruses X Z Y that is this
angle so this is also equal so therefore
these two triangles are congruent so
this is as per which criteria now is it
a right angle triangle no so RHS
criteria is gone
are we talking only about the sides no
so SSS criterion is also 1 we are
talking about two sides and one and that
to the angle is included between the two
sides right so therefore we are
definitely talking about the SAS
criterion question number two you want
to show that triangle a RT is congruent
to angle B en if you have to use SSS
criteria let's say that they are
congruent by SSS
then you need to show that a R is equal
to a R that is this side should be equal
to its corresponding side which is this
side that is a are should be equal to PE
RT that is this side should be equal to
the corresponding side that is this side
so this should be equal to en again 8 P
that is this side should be equal to the
corresponding side which is P n so ap
should be equal to P n now if it is
given that angle P is equal to angle a
that as this angle is equal to this
Anthony and you have to prove the
congruence using SAS criteria that means
side-angle-side you need to have RT is
equal to four side-angle-side if this is
the angle then which are the signs that
include this angle R T and a T right so
therefore RT should be equal to the
corresponding side which is e n that is
our T should be equal to e and and this
side the other side that is AP should be
equal to PM so here PM should be equal
to 8 so when you do this then you prove
it by SAS criteria question number three
inch angle ABC angle a equals 30 degree
angle P is equal to 40 degree and angle
C is equal to 110 degree so let us draw
a rough figure for the strangle so let's
say we have this triangle let us call
this angle a as 30 degree let us call
this as angle B which is 40 degree and
let us call this as angle C which is 110
degree so this is triangle ABC in
triangle PQR so this is another triangle
where you see the angles are the same
basically okay so let us say we draw
another triangle where angles are same
when we say angle R is equal to 110
degree and Q is equal to 40 degree and
angle P is equal to 30 degree so that
means we have to basically have two
triangles such that all their
corresponding angles are equal now a
student says that triangle ABC is
congruent to triangle PQR by a a a for
through and criteria if he justified why
or why not now first of all let me ask
you something do we have something
called a a
the wins criteria did we learn anything
like this no so that means the student
is taking wrong but the question is why
don't we have something like a a a
congruence criteria why is it that even
if all the three angles when all the
three sides of a triangle are equal then
the two triangles are congruent but when
all the three angles of two triangles
are equal then why the two triangles are
not congruent let me explain this now in
this case itself you see the triangle
ABC is smaller in size the triangle PQR
but still they have the same angles
right so even with the same angles even
if all the three angles have seen you
can alter the size of the triangle the
moment you alter the size of two
triangles they will move would be
congruent because congruence is all
about shape and size now if I want I can
draw a triangle very small maybe a
smaller triangle like this with the same
angles that is 40 degree hundred ten
degree and thirty degree but do you
think that this triangle will be
congruent to this triangle no because
they will never cover each other
completely because they have different
sizes so therefore we do not have
anything like a a a congruence criteria
so it does not exist because we can draw
triangles of different sizes even with
same angles but that is not true for SSS
because if this length of the three
sides are given and you can only draw
one particular size of a triangle with
those three sides because you really
cannot play around with the angles even
even if you try to change the angles the
three sides will not meet so that means
you can never draw multiple sizes of
triangles with the same sights so there
therefore we have a congruence criteria
for SSS but there is no congruence
criteria for AAA so we can say that he
is not justified and I hope I answered
why he is not justified question number
four in the figure the two triangles
when the corresponding parts are marked
we can write triangles at 80 is 122 so
we basically need to find the
corresponding parts so what do we see we
see that angle R is equal to angle W we
also see that after t is equal to angle
m and we see that angle a is equal to
angle Oh
so this shows that point R corresponds
to point W this shows that point T
corresponds to point N and this shows
that point a corresponds to point O so
if we write R 18 so this will be
congruent to our corresponds to W a
corresponds to O and T corresponds to n
so we will say that triangle add a T is
congruent to triangle w om good thank
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