This is known from the special structures of E 1, E2 and E3.

The combination coefficient of linear representation of ai is the component of ai.

So there is (a 1, a2, a3)=(e 1, e2, e3) a.

For example, in R 2, A 1 = (1, 24) t and A2 = (3 3,4) t.

Then a 1 = e 1+2e2, a2 = 3e 1+4e2.

So (a 1, a2) = (e 1, e2) *

1 3

2 4

= (e 1，e2)A