Using Algebraic Expressions for Formulas Video Lecture | Mathematics for Grade 7

hello friends this video on algebraic
expressions part 12 is brought to you by
exam viacom no more fear from exam so we
have been talking about algebra
expressions adding them subtracting them
and so many things about them now do you
think that you can find the value of an
algebraic expression it's difficult
right because when you think of an
algebraic expression it has both
variables and constants now as long as
we have a variables how can we find the
value of the iteration because we do not
know the value of the variables so
basically we can't find the value of an
algebraic expression only if we know the
value of the variable so for example in
this expression which is the variable X
so if we know the value of X then we can
find out the value of this expression
for example let's say that if the value
of x is equal to 1 then what would be
the value of the expression then the
value of this expression would be 3 into
1 minus 2 that is 3 minus 2 which is
equal to 1 if the value of x is equal to
do then what will happen then this
expression will be equal to 3 into 2
minus 2 that is 6 minus 2 which is equal
to 4 so the value of the expression
changes with the value with the changing
values of the variable so if we know the
value of the variable we can definitely
find the value of the expression so let
us try to find values of some algebraic
expression so let's say that if P is
equal to minus 2 find the value of minus
3 P squared plus 4 P plus 7 so let's try
to find this value so minus 3 P square
that actually means minus 3 into P into
P plus 4 into P plus 7 now the value of
P is given as minus 2 so let us replace
P with minus 2 so this is what we get
now let us try to solve this so 3 into 2
into 2 that would be 12 so if you have
how many minus sign
three - and so the product will have a
minus sign for in 2 minus 2 would be
minus 8 plus 7 so this would be equal to
minus 12 minus 8 plus 7 so when you add
these two what do you get 20 but it
would have a negative sign because both
of them have negative sign plus 7 so
this would be equal to minus 13 so minus
13 is the value of this expression so we
were able to find this value only
because the value of P which is the
variable in this expression is given
here
let's try another example if a is equal
to 2 B is equal to minus 2 find the
value of a square plus B Square okay so
a square would mean a into a plus B
Square would mean B into B so the value
of a is given as 2 so 2 into 2 plus
value of B is minus 2 so minus 2 into
minus 2 so this would be 4 and minus 2
into minus 2 put on so before so 4 plus
4 would be 8 so 8 would be the value of
this expression now you might wonder
that why are they studying so much about
algebraic expressions and these
algebraic expressions going to help us
in any way so that's a very common
question that might strike your man so
why are we studying this okay now let me
give you an example now we all know that
we need to find out certain values in
our day-to-day life for example if you
have a rectangular field you might need
to calculate the area of that field or
if you have maybe a field which is in
the shape of a square and you want to
fence your field that is you want to put
a boundary to your field so you need to
calculate the boundary of the square or
the perimeter of the square so when you
want to calculate these kind of things
like finding the perimeter of a square
that is the total length of the boundary
or the area of a rectangle so what do
you do so let us look at this so this is
the square which has
sites equal fine so how do you find the
perimeter of the square so we know that
perimeter is nothing but the total
boundary so the total boundary in this
case would be the length of this side
plus this side plus this side plus this
side
so the perimeter would be side plus side
plus side plus like that this side added
four times because there are four equal
signs so this is nothing but four into
side because side is being added four
times now let us say it is assumed that
the length of each side is L so let's
say we do not know because the length of
the science of different squares might
be different so let us assume that the
length of each side of the square is L
so in that case we can see that the
perimeter of the square is given by 4 n
now as you keep changing the value of L
the perimeter of the square keeps
changing so what does this for n so 4l
is the formula to calculate the
perimeter of the square why do we need
this formula so that our task of
calculation becomes easier all you need
to do is doesn't matter whatever the
size of a square is all you need to do
is just put the value of L and you
calculate the perimeter and what does
this for n this for L is nothing but an
algebraic expression similarly when you
try to calculate the area of a rectangle
so how much is the area of a rectangle
we calculated like this length into
breadth where L is the length and B is
the breadth so if you know length and
breadth of any rectangle you can quickly
calculate its area but what is this
length into breadth this is nothing but
an expression again because it contains
variables it contains operators so this
is also an example of an expression
so these interpret expressions they are
widely used in making formula and the
formula becomes easier to be represented
so instead of if you represent perimeter
of a square a side plus side plus I
percent or if you represent it you
present it as 4l which is more simpler
and easier to represent obviously for N
and what is that for n nothing but an
expression so algebraic expressions make
the representation of your formula
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