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Question 2
Showing the ${{\left( r+1 \right)}^{\text{th}}}$ term is even
In the expansion of ${{\left( 1-2b \right)}^{n}}$ in ascending powers of $b$, the coefficient of the third term is $112$.
(a)
Find the value of $n$.
(b)
Without writing the expansion of ${{\left( 1-2b \right)}^{n}}$, explain why the coefficient of the ${{\left( r+1 \right)}^{\text{th}}}$ term is an even number.
(a)
(b)
