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Solution

We know $\omega^3 = 1$ and $1 + \omega + \omega^2 = 0$. So $1 + \omega = -\omega^2$. Hence $(1 + \omega)^7 = (-\omega^2)^7 = (-1)^7 \omega^{14} = -\omega^{14}$. Now $\omega^{14} = \omega^{3 \times 4 + 2} = \omega^2$. Therefore $(1 + \omega)^7 = -\omega^2 = 1 + \omega$. So comparing with $A + B\omega$, we have $A = 1$, $B = 1$. $\Rightarrow A + B = 2.$