A determinant is a scalar value that is calculated from a square matrix. It provides important information about the matrix, such as whether it can be inverted, the volume scaling factor of the linear transformation it represents, and whether a system of linear equations has a unique solution.
A zero determinant indicates that the matrix is singular, meaning it does not have an inverse. For a system of linear equations, this implies that the system does not have a unique solution; it may have either no solutions or infinitely many solutions.
A minor is the determinant of a submatrix formed by deleting one row and one column from the original matrix. The cofactor is the minor with a sign attached, depending on its position: (-1)i+j times the minor of element aij.
Determinants are a fascinating concept in linear algebra that helps us understand and solve matrix equations. Imagine you have a set of linear equations, and you want to find if they have a unique solution. Determinants give you a quick way to check this. They are like a special number that can tell us a lot about a matrix, such as whether it has an inverse or if the system of equations it represents has a unique solution. In essence, determinants are powerful tools that simplify complex matrix operations and provide deep insights into the structure of linear systems.
In this article, you'll discover practical tips and tricks for using determinants to solve matrix problems easily. With clear examples and illustrations, we'll help you tackle determinant challenges confidently.
1.0Determinants Definition
It is the value associated with the square arrangement of numbers in rows and columns written in between two parallel lines.
For every square matrix A = aij of order n, we can assign a number (real or complex) known as the determinant of the matrix A. Here, aij represents the element in the i-th row and j-th column of A. This determinant is a special value that provides critical information about the matrix, such as whether it can be inverted, the volume scaling factor of the linear transformation it represents, and whether a system of linear equations possesses a unique solution.
Ex- a1a2b1b2
A determinant of second order consists of two rows and two columns.
a1a2a3b1b2b3c1c2c3
A determinant of third order or 3 × 3 consists of three rows and three columns.
Minors of an element is defined as the minor determinant obtained by deleting a particular row or column in which that element lies. Ex. in the determinant
D=a11a21a31a12a22a32a13a23a33 minor of a12 denotes as M12
M12=a21a31a23a33 and so on
5.0Cofactor
Cofactor of an elements aij is expressed as Cij and is calculated as:
Cij = (–1) i+j Mij, Where ‘i’ denotes the row and j denotes the column.
Note: That a determinant of order 3 will have 9 minors, each minor will be a determinant of order 2 and a determinant of order4 will have 16 minors each minor will be a determinant of order 3.
Expansion of a determinant in Terms of the Elements of any Row or column
D=∑i=13aijCij etc. for i=1,2,3
Sum of the product of elements of any row (column) with cofactors of corresponding elements of any other row (column) is ZERO.
6.0Properties of Determinants
Property 1: The value of a determinant stays the same if the respective row and columns are interchanged.
Property 2: If any 2 rows (or columns) of a determinant are interchanged, the value of determinant is changed in sign only.
Property 3: If a determinant has any two identical rows (or columns), its value is zero.
D=a1a1a3b1b1b3c1c1c3= 0
Property 4: If all the elements of a row (or column) are multiplied by a scalar, the determinant is multiplied by that scalar.
If D=a1a2a3b1b2b3c1c2c3 and D1=Ka1a2a3Kb1b2b3Kc1c2c3
then D1 = KD
Note: |K D|=K^n .|D| where n is the order of determinants and K is a scalar.
Property 5: If each element of a row (or column) can be written as the sum of two terms, the determinant can be expressed as the sum of two determinants.
Note: Multiplication of 2 matrices is only possible with Row - column Method, while multiplication of 2 determinants can be done with R-R , C-C, C-R and R-R method also.
Example 2: Find the minors and cofactors of elements '-3', '5', '–1' and '7' in the determinant 24−1−306157.
Solution:
Minor of −3=4−157=33; Cofactor of −3=−33 Minor of 5=2−1−36=9; Cofactor of 5=−9 Minor of −1=−3015=−15; Cofactor of −1=−15 Minor of 7=24−30=12; Cofactor of 7=12
Example 3: If Dr=rn2n(n+1)r3n3(2n(n+1))222n2(n+1), find ∑r=0nDr,find∑r=0nDr.