Data 605 Week 2 Discussion Board Example

Chapter D - Determinants

Exercise C21

Doing the computations by hand, find the determinant of the matrix below.

cat("Matrix A", "\n", "\n")

## Matrix A 
## 

(A = matrix (c(1,3,6,2), ncol = 2, byrow = TRUE))

##      [,1] [,2]
## [1,]    1    3
## [2,]    6    2

The formula for finding the determinant for a 2x2 matrix is |A| = ad - bc

First, we find the values of ad by multiplying 1 x 2

(AD <- A[1,1] * A[2,2])

## [1] 2

Next, we find the values of bc by multiplying 3 x 6

(BC <- A[1,2] * A[2,1])

## [1] 18

Lastly, we subtract ad from bc

(AD-BC)

## [1] -16

Using the built-in features from base R we can check our work

det(A)

## [1] -16