# Matrix determinant problem

TW Cantor

## 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.

## 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 dont understand what the I and the m are representing

## Answers and Replies

icystrike
I= [1,0]
[0,1]

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

Can u combine A-mI into a single 2 by 2 matrix?:grumpy:
(With that u can find the determinant like how u always do)

TW Cantor
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 :-)