# Direct sum and product representation

1. May 24, 2013

### Yoran91

Hi everyone,

I'm having some trouble with the concept of the direct sum and product of representations.
Say I have two representations $\rho_1 , \rho_2$ of a group $G$ on vector spaces $V_1, V_2$ respectively. Then I know their direct sum and their product are defined as

$\rho_1 \oplus \rho_2 : G \to GL\left(V_1 \oplus V_2 \right)$
with $\left[\rho_1 \oplus \rho_2 \right] (g) (v_1,v_2) = (\rho_1 (g) v_1 ,\rho_2 (g) v_2)$

and

$\rho_1 \otimes \rho_2 : G to GL\left(V_1 \otimes V_2 \right)$
with $\left[ \rho_1 \otimes \rho_2 \right] (g) v_1 \otimes v_2 =\rho_1 (g) v_1 \otimes \rho_2 (g) v_2$.

However, in calling these maps representations I have to show these are homomorphisms, which I can't seem to do. Can anyone help?

EDIT: Nevermind, I worked it out.

Last edited: May 24, 2013