Then a 3+8e = 10e.

Obtained from the cubic sum formula

(A+2E)(A^2+2A+4E^2)= 10E

that is

(A+2E)(A^2+2A+4E^2)/ 10=E

So from the definition of inverse matrix, we can know that,

+2E is reversible,

And (a+2e) (-1) = (a 2+2a+4e 2)/10.