Question

if a=(123 456 789) find a11+a31-a22

Answer 1

Given a square matrix, the cofactor of a

ij

is denoted by A

ij

=(−1)

i+j

M

ij

, where M

ij

is the minor of the entry a

ij

M

ij

=

∣

∣

∣

∣

∣

∣

2

6

5

4

∣

∣

∣

∣

∣

∣

From the matrix, a

32

=5

Determinant of A

32

=(−1)

3+2

∣

∣

∣

∣

∣

∣

2

6

5

4

∣

∣

∣

∣

∣

∣

=−(−8−30)=22

Therefore, a

32

.A

32

=5×22=110.