Recurrence Relations

Recurrence Relations

TGM Original Questions

Recurrence Relations

A recurrence relation is an equation that recursively defines a sequence. Each term of the sequence is defined as a function of preceding terms.

Recurrence relationHow the next term is obtainedFirst terms
\(x_{n+1}=\sqrt{x_n+5},\ x_0=1\)Add \(5\), then take the positive square root.\(1,\sqrt6,\sqrt{\sqrt6+5},\ldots\)
\(u_{n+1}=0.5u_n+8,\ u_1=4\)Halve the current term, then add \(8\).\(4,10,13,14.5,15.25,\ldots\)
\(a_n=a_{n-1}+k,\ a_0=3\)Add the constant \(k\).\(3,3+k,3+2k,3+3k,\ldots\)
\(u_n=-2u_{n-1},\ u_0=3\)Multiply the current term by \(-2\).\(3,-6,12,-24,48,\ldots\)
\(T_n=T_{n-1}+T_{n-2},\ T_1=0,\ T_2=1\)Add the preceding two terms.\(0,1,1,2,3,\ldots\)

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Answer:(1) Add \(5\), then take the square root: \(1,\ 2.4495,\ 2.7294,\ 2.7802,\ 2.7893\), increasing (2) Multiply by \(0.5\), then add \(8\): \(4,\ 10,\ 13,\ 14.5,\ 15.25\), increasing (3) Add \(k\): \(3,\ 3+k,\ 3+2k,\ 3+3k,\ 3+4k\), increasing for \(k>0\), constant for \(k=0\), decreasing for \(k<0\) (4) Multiply by \(-2\): \(3,\ -6,\ 12,\ -24,\ 48\), alternating (5) Add the preceding two terms: \(0,\ 1,\ 1,\ 2,\ 3\), non-decreasing

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