r-2 1 -2
-5 r+3 -3
1 0 r+2
c1+c2-c3
r+1 1 -2
r+1 r+3 -3
-r-1 0 r+2
r2-r1,r3+r1
r+1 1 -2
0 r+2 -1
0 1 r
= (r+1)[r(r+2)+1]
= (r+1)(r^2+2r+1)
= (r+1)^3.