Maths Simple Equation part 3 (Setting up Equation) CBSE Class 7 Mathematics VII Video Lecture | Extra Documents & Videos for Class 7

hello friends this video on simple
equations part 3 is brought to you by
exam fee or comm know about fear from
exam so now let's start setting up an
equation so how do we set up an equation
how to be make an equation now there are
certain simple rules that we will follow
to set up an equation now for all of
these just follow these steps and you
will be able to set up the equation very
well now let's say that you have a
problem statement that pirates code 2
marks more than twice the mark scored by
Roman pilots score is 20 what does no
one score so we want to know Roman
school now the first step is that for
any value that you need to find or you
do not know consider that as a variable
so in this case what is that thing which
we do not know pyon score you already
know rojan score is something which we
do not know so what we will do as per
step 1 we will assume Rohan's score to
be a variable let us say that variable
is X so let draw once for B X that is
our first step for any value that we do
not know what we will have to find that
value we will assume that as a variable
fine
the second step is set of expressions as
per the conditions in the question now
the question will definitely have some
condition or criteria so in this case
what is the condition it sees that piles
code 2 marks more than twice the marks
code by row 1 so this is the condition
given in the question so this is the
criteria so let us make that expression
as for this the score of pile that means
pile score should be as but this
condition it should be 2 marks more than
twice the mark scored by Roman so twice
the marks of rohan would be 2x plus 2
because 2 much more than that so as for
the condition piles code should be 2
plus 2x and the final step is equates
the expressions equate with what equate
with whatever value is given in the
question
for
the hair piled score is already given as
20 so what will be equate we really
equate 2x plus 2 is equal to 20 because
this is the this aspire score as per our
assumption and this is actual pilots
code so 2x plus 2 is equal to 20 so this
is how we set up an equation now how do
I solve this equation that is something
which we will take up in the later
section so for now you just understand
how do we set up an equation so three
simple steps to set up an equation first
you assume an unknown value to be a
variable say it create expressions as
per the conditions given in the question
third equate the expressions to form an
equation so let us now try to set up
equation for a couple of examples let's
consider this example one Laxmi is
father is 49 years old okay this is
something which is already given he is 4
years older than 3 times lections age
okay so this is basically our condition
the second statement is nothing but the
condition so what is that value which we
do not know so here also we will follow
step by step in step 1 we will first
assume that value to be X which we do
not know so we already know Laxmi is
father's age but we do not know Laxmi
age so let us assume that Laxmi is age
is X so our first step is done now let's
move on to step 2 it says that we will
have to build expressions for the
condition so what is the condition it
says that father is 4 years older then 3
times Laxmi is age so 3 times Laxmi is H
is 3 X 4 years older than that that
means 3 X plus 4 so this should be
father's age as for the conditions given
in the question perfect now let's move
on to step 3 so in step 3 what are we
going to do we are going to equate the
expressions so 1 inspiration is 3x plus
4 which is father's age
the question father's age is already
given as 49 so 3x plus 4 should be equal
to 49 so this is our equation for this
problem statement so this is how we set
up equations let's look at one more
example in an isosceles triangle the
vertex Apple is twice either base angle
so this gives you the relationship or
the criteria remember that the sum of
the angles of a triangle is 180 degrees
now let us first understand everything
term by down now what do we mean by
isosceles triangle so isosceles triangle
is a triangle where two sides are equal
so let us see if we have a triangle ABC
such that the length of a B is equal to
the length of AC so if a B is equal to
AC then we say that ABC is an isosceles
triangle
so in either sillas triangle two sides
are equal
now these two angles are also equal that
is angle ABC is equal to angle ACB so
these are the properties of isosceles
triangle now these two angles are called
the base angles because they are located
at the base and this angle the third
remaining angle is called the vertex
angle clear so now we understand what is
the base angle what is vertex angle in
an isosceles triangle now what is there
the question what is that angle which we
do not know so in this case we do not
know the base angle you also do not know
the vertex angle we do not know any of
them so what do we do now when we look
at the criteria or when we look at the
relationship we see that it sees that
vertex angle is twice either phase angle
now both the base angles are going to be
the same so in step one what do we do we
assume let us assume that the base
angle which is equal to angle B or angle
ABC which is also equal to angle ACB let
us assume that the space angle is equal
to X so we have assumed so our first
step is over in second step let's make
mathematical expression based on the
condition that is given so the condition
is vertex angle is twice either base
angle so the vertex angle as per this is
vertex angle will be equal to twice the
value of each base angle so it will be
2x perfect now in the third step what do
we do in step three we is that we equate
the expressions right so we have a
vertex angle is 2x and we have a
relationship that sum of all the three
angles of a triangle is 180 degree that
means angle ABC plus angle ACB plus
angle B AC this is equal to 180 degrees
this is something that we know by
properties of triangle so angle ABC
what is angle ABC ABC is a base angle
which is H which we have assumed is X
what is ACB ACB is a in base angle which
is X what is BAC BAC is the vertex angle
which is 2x so this is equal to 180
degrees therefore X plus X plus 2x which
is equal to 4x is equal to 180 degree so
this is going to be the equation for
this problem statement so you see here
it was slightly different but again we
followed the same three steps then we
could arrive at the equation thank you
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