[Music]

welcome to WWE collegiate comm viewers

and subscribers today I am going to

discuss about a problem so how to crack

that problem in 30 seconds so why do we

solve in 30 seconds the problem because

in competitive entrance examination we

have only stipulated time in limited

time we are asked to solve more than 80

or sometimes 100 problems in the

examination so that is also moreover the

multiple choice questions so that is why

we have to improve our speed and

accuracy so in order to enhance our

speed and accuracy it had better to

remember formulae concepts as well as

some in addition to them some techniques

after we developed so while following

the problems so that is why regarding

that actually here so I would like to

construct them some problems how to

solve some problems in 30 seconds so in

this session or in this episode so I

give more emphasis on how to crack a

inverse problem in mathematics are how

to find out the inverse a inverse in 30

seconds okay shall we discuss that

problem okay before going to do the

problem so you know the virginal method

so because let us analyze the original

method and after that we discussed the

problem in 30 seconds we shall read okay

so if you want to find out the inverse

of a square matrix a suppose a whose

order is 3 by 3 generally what do you do

so we have to find out which is a

determinant so that is dead a if decay

does not equal to 0 then we know that

is known as non singular matrix then it

possesses inverse a inverse exists so

what we have to do next step we have to

find out adjoint of a the adjoint of a

can be evaluated using the all the

cofactors of the element that you're

monitoring you might be practiced by

reading your board examinations so also

getting adjoint a we have one formula a

inverse is equal to 1 by DT into a G so

this is the actually process has to be

followed it may take more than three

minutes or five minutes in the

examination but totally so this problem

how to do in 30 seconds in this session

we shall discuss so first problem the

inverse of a is equal to 3 5 7 2 minus 3

1 1 1 2 e first option second option

third option for suction so now let me

explain the shortcut so how to find out

the shortcut means first take this

middle element

are you following then you read on like

this minus 3 1 2 minus 3 next dump here

1 2 1 1

next up similarly take middle element

you write on like this 5 7 3 5 next

again same top row as it is no Don minus

3 1 2 minus 3 now here see this is 2 by

2 matrix 2 by 2 matrix 2 by 2 matrix 2x2

2x2 2x2 just 2 by 2 matrix determinants

we have to calculate that is you know ad

minus BC formula so I write again minus

6 minus 1 minus 7 1 minus 4 minus 3

2 + 3 5 correct chicked 7 minus 10 minus

3/7 minus 10 minus 3 6 minus 7 minus 1

okay 5 minus 3 - correct

okay now Phi plus 21 26 okay I might be

doing correctly 14 minus 311 so you have

to practice speed that is only - nine -

ten - 19 now for the bracket do you know

what does it represent it is nothing but

cofactor matrix now adjoint of a

directly we'll get it even as giant of

matrix also we can find out that is

transpose of this one transpose this is

adjoint of method get the transpose

transpose means - 7 - 3 5 - 3 - 1 to 26

Levin and - 90 but what is our aim to

find out a inverse to find out a inverse

at G a is multiplied by 1 by DT so now

we have to calculate a dta I will

explain how to find out DT DT a is equal

to r1 not a multiplied c1 of AD GA c1 of

ad g r1 r1 means 3 5 7 3 5 7 multiplied

by C one column of Ag column of a G is

-7 - 3 5 so this is

row by column minus 21 minus 15 plus 35

35 minus 15 is how much 35 minus 15 is

plus 20 minus 21 plus 20 minus 1 so that

means a inverse is equal to I will tell

you here a inverse is equal to 1 by ei

into a G so that means we have to

multiply this 1 is minus 1 so if you

multiply it minus 1 what you get now 7 3

minus 26 3 1 minus 11 minus 5 minus 2 90

just now coming to the options check for

the options so which is the right option

yes second one is the reservation that's

very very important one very very easy

shortcut you might have fired

you