C22 on Page 388

B <- matrix(c( 2, 1, -1, 1), 2, 2, byrow = TRUE)

B

##      [,1] [,2]
## [1,]    2    1
## [2,]   -1    1

ev <- eigen(B)

ev$values

## [1] 1.5+0.866025i 1.5-0.866025i