Asked: If \(a_1 = 1\) and \(a_{n+1} – 3a_n+ 2 = 4n\) for every positive integer n, then \(a_{100}\) equals
In general
\(a_n = 3ˆn - 2n\)
\(a_{n+1} = 3ˆ(n+1) - 2(n+1)\)
\(a_{n+1} = 3(3ˆn - 2n) + (4n-2) = 3ˆ(n+1) - 6n + 4n - 2 = 3ˆ(n+1) - 2(n+1)\)
\(a_100 = 3ˆ100 - 2*100 = 3ˆ100 - 200\)
IMO C
In general
\(a_n = 3ˆn - 2n\)
\(a_{n+1} = 3ˆ(n+1) - 2(n+1)\)
\(a_{n+1} = 3(3ˆn - 2n) + (4n-2) = 3ˆ(n+1) - 6n + 4n - 2 = 3ˆ(n+1) - 2(n+1)\)
\(a_100 = 3ˆ100 - 2*100 = 3ˆ100 - 200\)
IMO C