Math Problem Statement

The rule for a sequence is given as u_{n+2} = u_{n+1} + u_n. Given that u_1 = u_2 = 1, list the first eight terms of this sequence. What is the sequence called? In which position is the number 233 in this sequence?

Solution

Let's analyze and solve the problem.

We are given the recurrence relation for a sequence un+2=un+1+unu_{n+2} = u_{n+1} + u_n, with initial conditions u1=1u_1 = 1 and u2=1u_2 = 1.

Part (a): Listing the first eight terms of the sequence

Using the recurrence relation, we can compute each term as follows:

  • u1=1u_1 = 1
  • u2=1u_2 = 1
  • u3=u2+u1=1+1=2u_3 = u_2 + u_1 = 1 + 1 = 2
  • u4=u3+u2=2+1=3u_4 = u_3 + u_2 = 2 + 1 = 3
  • u5=u4+u3=3+2=5u_5 = u_4 + u_3 = 3 + 2 = 5
  • u6=u5+u4=5+3=8u_6 = u_5 + u_4 = 5 + 3 = 8
  • u7=u6+u5=8+5=13u_7 = u_6 + u_5 = 8 + 5 = 13
  • u8=u7+u6=13+8=21u_8 = u_7 + u_6 = 13 + 8 = 21

Thus, the first eight terms are:

u1=1, u2=1, u3=2, u4=3, u5=5, u6=8, u7=13, u8=21.u_1 = 1, \ u_2 = 1, \ u_3 = 2, \ u_4 = 3, \ u_5 = 5, \ u_6 = 8, \ u_7 = 13, \ u_8 = 21.

Part (b): Name of the sequence

This sequence is known as the Fibonacci sequence.

Part (c): Position of the number 233 in the sequence

Continuing the sequence from u9u_9 onward:

  • u9=u8+u7=21+13=34u_9 = u_8 + u_7 = 21 + 13 = 34
  • u10=u9+u8=34+21=55u_{10} = u_9 + u_8 = 34 + 21 = 55
  • u11=u10+u9=55+34=89u_{11} = u_{10} + u_9 = 55 + 34 = 89
  • u12=u11+u10=89+55=144u_{12} = u_{11} + u_{10} = 89 + 55 = 144
  • u13=u12+u11=144+89=233u_{13} = u_{12} + u_{11} = 144 + 89 = 233

Thus, the number 233 appears at position 13 in the sequence.


Do you have any questions or need further clarification?

Here are 5 related questions to explore:

  1. What is the closed-form formula for the Fibonacci sequence?
  2. How can you generalize the recurrence relation to different initial conditions?
  3. What is the relationship between Fibonacci numbers and the golden ratio?
  4. Can you derive a formula to calculate the nn-th Fibonacci number directly?
  5. How can Fibonacci numbers be found in nature and art?

Tip: The Fibonacci sequence is often used to model growth patterns, such as in population studies or natural phenomena like spirals in shells and flowers.

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Math Problem Analysis

Mathematical Concepts

Recurrence Relations
Fibonacci Sequence

Formulas

u_{n+2} = u_{n+1} + u_n

Theorems

Fibonacci Theorem

Suitable Grade Level

Grades 8-10