excercise C20 page 190

A <- matrix(c(2,-1,2,5,3,-2), nrow=3, ncol=2) 
A
##      [,1] [,2]
## [1,]    2    5
## [2,]   -1    3
## [3,]    2   -2
B <- matrix(c(-1,2,5,0,-3,2,4,-3), nrow=2, ncol=4) 
B
##      [,1] [,2] [,3] [,4]
## [1,]   -1    5   -3    4
## [2,]    2    0    2   -3
A %*% B
##      [,1] [,2] [,3] [,4]
## [1,]    8   10    4   -7
## [2,]    7   -5    9  -13
## [3,]   -6   10  -10   14