For n Z+, find in (1 + x + x2)(1 + x)n the coefficient of (a)

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For n ∈ Z+, find in (1 + x + x2)(1 + x)n the coefficient of
(a) x7;
(b) x8; and
(c) xr for 0 < r < n + 2, r ∈ Z.
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