a<-matrix(c(3,1,7,5,6,2,9,9,7,3,4,6,1,5,8,4),nrow=4,ncol=4,byrow=T)
a
b<-matrix(c(5,9,7,3,6,8,8,5,4,6,2,7),nrow=4,ncol=3,byrow=T)
b
amb<-a%*%b
amb
tbma<-t(b)%*%a
tbma
ainv<-solve(a)
ainv
iden<-a%*%ainv
iden

A<-matrix(c(2,3,0,3,0,-2,1,2,1),nrow=3,ncol=3,byrow=T)
A
H<-matrix(c(24,5,17),nrow=3,ncol=1)
H
Ainv<-solve(A)
Ainv
X=Ainv%*%H
X