find the coefficient of x^5 in the expansion (x+2)(x+1)^8

3 answers

x* (x+1)^8
+
2(x+1)^8
so
find coef of x^4 in (x+1)^8
find 2*coef of x^5 in (x+1)^*
add them
from binomial coefficient table
(x+1)^8 = x^8 ..... 56x^5+70x^4....+1
so 70 + 2(56) = 182
182 is the final answer? Thank you for your help.
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