library(Matrix)
## Warning: package 'Matrix' was built under R version 4.3.2

A <- matrix(c(-1, 2, -6, 6), nrow = 2, byrow = TRUE)

eigen(A)
## eigen() decomposition
## $values
## [1] 3 2
## 
## $vectors
##            [,1]       [,2]
## [1,] -0.4472136 -0.5547002
## [2,] -0.8944272 -0.8320503