What is the determinant of a matrix with a variable?

Click For Summary
SUMMARY

The discussion focuses on calculating the determinant of the matrix A, defined as [25, 5; -150, -30], in terms of a variable m. The determinant is computed using the formula det(A) = ad - bc, leading to the conclusion that the matrix is singular when det(A) equals zero. The expression for det(A - mI) is derived as m² + 5m, where I represents the identity matrix. This quadratic expression in m is essential for understanding the behavior of the matrix as m varies.

PREREQUISITES
  • Understanding of matrix operations, specifically determinant calculation.
  • Familiarity with identity matrices and their properties.
  • Knowledge of quadratic equations and their characteristics.
  • Basic linear algebra concepts.
NEXT STEPS
  • Study the properties of determinants in linear algebra.
  • Learn about singular matrices and their implications.
  • Explore the derivation and applications of quadratic equations.
  • Investigate the role of identity matrices in matrix transformations.
USEFUL FOR

Students in linear algebra, mathematicians, and anyone seeking to deepen their understanding of matrix determinants and their applications in various mathematical contexts.

TW Cantor
Messages
53
Reaction score
1

Homework Statement


The matrix A is given as:
[25 , 5]
[-150 , -30]

find, in terms of m, the expression det(A-mI). This will be in a quadratic expression in m.

Homework Equations



det(A) = ad-bc

The Attempt at a Solution



i have no idea how to approach this but i worked out the det(A) using the equation above to be 0. This makes this matrix singular. I don't understand what the I and the m are representing
 
Physics news on Phys.org
I= [1,0]
[0,1]

mI= [m,0]
[0,m]

Can u combine A-mI into a single 2 by 2 matrix?
(With that u can find the determinant like how u always do)
 
ahhh yes i get it now. if i do A-mI and then calculate the determinant of that new matrix then i get: m2 + 5m.

thanks a lot :-)
 

Similar threads

  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 23 ·
Replies
23
Views
2K
Replies
3
Views
2K
  • · Replies 32 ·
2
Replies
32
Views
3K
  • · Replies 69 ·
3
Replies
69
Views
11K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 9 ·
Replies
9
Views
5K
  • · Replies 7 ·
Replies
7
Views
4K
  • · Replies 14 ·
Replies
14
Views
5K