library(matlib)

A <-matrix(c(1,2,1,1),nrow=2,ncol=2)

A

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

b <-c(4,5)
b

## [1] 4 5

Solve(A,b)

## x1    =  1 
##   x2  =  3

plotEqn(A,b)

##   x[1] + x[2]  =  4 
## 2*x[1] + x[2]  =  5

A2 <-matrix(c(1,-2,-1,2,3,2,3,-2,1),nrow=3,ncol=3)
b2 <-c(6,-1,2)
Solve(A2, b2)

## x1      =  1 
##   x2    =  1 
##     x3  =  1

v=plotEqn3d(A2,b2, xlim=c(0,4),ylim=c(0,4))
v