Answer:
Step-by-step explanation:
since we know that in this expansion is
thus
Hope that helps!
a₂₁ = 638
substitute n = 21 into the explicit formula
a₂₁ = - 2 + 32(21 - 1) = - 2 + 32(20) = - 2 + 640 = 638
i think b or d
3(x+9)
3 multiply both x and 9
3x+27
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