MathChapter 12: Composition, Recursion, and Exponential Functions
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Prompt
What two parts does a recursive definition require?
Answer
An initial condition and a recurrence rule.
Prompt
What does an initial condition do?
Answer
It states the starting term and its index.
Prompt
What does a recurrence rule do?
Answer
It defines a new term from one or more preceding terms.
Prompt
What term follows \(a_0\)?
Answer
\(a_1\).
Prompt
What term follows \(a_1\)?
Answer
\(a_2\).
Prompt
In \(a_n=a_{n-1}+4\), which value is used to find \(a_n\)?
Answer
The immediately preceding term \(a_{n-1}\).
Prompt
Should the initial term be reused at every recursive step?
Answer
No. Each newly calculated term becomes the next previous term.
Prompt
Why calculate intermediate terms explicitly?
Answer
They prevent skipped-state and index-shift errors.
Prompt
What does \(a_n=2a_{n-1}\) do each step?
Answer
It doubles the previous term.
Prompt
What does \(a_n=a_{n-1}+n\) require besides the previous value?
Answer
The current index \(n\).
Prompt
How is repeated self-composition recursive?
Answer
Each function output becomes the input for the next application of the same function.
Prompt
What does \(f(f(f(x)))\) require?
Answer
Three sequential applications of \(f\), recording each intermediate output.
Prompt
In \(A_n=1.02A_{n-1}+50\), which operation happens first?
Answer
Multiply the previous amount by \(1.02\), then add \(50\).
Prompt
What would \(1.02(A_{n-1}+50)\) mean instead?
Answer
Add \(50\) first, then multiply the entire sum; it is a different recurrence.
Prompt
Why delay rounding in a decimal recurrence?
Answer
Rounded intermediate states can accumulate error in later terms.
Prompt
Recursive versus explicit formula: what is the distinction?
Answer
A recursive rule depends on earlier terms; an explicit rule computes a term directly from its index.
Prompt
If \(a_0=2\) and \(a_n=3a_{n-1}+1\), find \(a_2\).
Answer
\(a_1=7\), then \(a_2=22\).
Prompt
If \(b_1=10\) and \(b_n=b_{n-1}-2n\), find \(b_3\).
Answer
\(b_2=6\), then \(b_3=0\).
Prompt
What three columns expose most recurrence mistakes?
Answer
Index, previous term, and substituted rule; a fourth column can record the new term.
Prompt
How do you validate a proposed recurrence from a list?
Answer
Check its initial index and test at least two consecutive transitions.
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