pdf("rpd2_6.pdf")

library(MASS)

A <- matrix(c(1,2,3,3,5,7),byrow=T,ncol=2)

y <- matrix(c(6,9,21),ncol=1)

ginv_A <- ginv(A)

x <- ginv_A %*% y

Aginv_AA <- A %*% ginv_A %*% A

A

y

ginv_A

x

Aginv_AA

dev.off()