High School Math : Summations and Sequences

Study concepts, example questions & explanations for High School Math

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Example Questions

Example Question #1 : Summations And Sequences

Consider the Fibonacci sequence written below. What are the next three terms?

\(\displaystyle \small 1,\1,\ 2,\ 3,\ 5,\ 8,\ 13,...\)

Possible Answers:

\(\displaystyle 18, \23,\ 28\)

\(\displaystyle 14,\ 17 ,\ 22\)

\(\displaystyle 16,\ 21,\ 24\)

\(\displaystyle 21,\ 55,\ 63\)

\(\displaystyle 21,\ 34,\ 55\)

Correct answer:

\(\displaystyle 21,\ 34,\ 55\)

Explanation:

Each number in the Fibonacci sequence can be calculated by the sum of the previous two numbers.

\(\displaystyle x_n=x_{n-1}+x_{n-2}\)

The next term in the sequence will be the sum of the two terms preceding it: 8 and 13.

\(\displaystyle x_n=13+8=21\)

\(\displaystyle \small 1,\1,\ 2,\ 3,\ 5,\ 8,\ 13,\ 21...\)

The next term will be the sum of 13 and 21.

\(\displaystyle x_n=21+13=34\)

\(\displaystyle \small 1,\1,\ 2,\ 3,\ 5,\ 8,\ 13,\ 21,\ 34...\)

The next term will be the sum of 21 and 34.

\(\displaystyle x_n=34+21=55\)

\(\displaystyle \small 1,\1,\ 2,\ 3,\ 5,\ 8,\ 13,\ 21,\ 34,\ 55...\)

Example Question #1 : Mathematical Relationships And Basic Graphs

Which of the following is a geometric sequence? 

Possible Answers:

\(\displaystyle t_{0}=10\) 

\(\displaystyle t_{n}=t_{n-1}+5\) 

\(\displaystyle t_{0}=2\) 

\(\displaystyle t_{n} = t_{n-1}^{6}\)

\(\displaystyle t_{0}=4\)

\(\displaystyle t_{n}=t_{n-1}+3.4\) 

\(\displaystyle t_{0}=4\) 

\(\displaystyle t_{n}=t_{n-1}\times 3\)

\(\displaystyle t_{0}=5\)

\(\displaystyle t_{n}=t_{n-1}+3\) 

Correct answer:

\(\displaystyle t_{0}=4\) 

\(\displaystyle t_{n}=t_{n-1}\times 3\)

Explanation:

A geometric sequence is one in which the next term is found by mutlplying the previous term by a particular constant. Thus, we look for an implicit definition which involves multiplication of the previous term. The only possibility is: 

\(\displaystyle t_{0}=4\)

\(\displaystyle t_{n}=t_{n-1}\times 3\)

Example Question #1 : Arithmetic Series

List the first 4 terms of an arithmetic sequence with a first term of 3, and a common difference of 5. 

Possible Answers:

\(\displaystyle 5, 10, 15, 20\)

\(\displaystyle 5, 8, 10, 13\)

\(\displaystyle 3, 8, 13, 18\)

Correct answer:

\(\displaystyle 3, 8, 13, 18\)

Explanation:

An arithmetic sequence is one in which the common difference is added to one term to get the next term. Thus, if the first term is 3, we add 5 to get the second term, and continue in this manner. 

Thus, the first four terms are: 

\(\displaystyle 3, 8, 13, 18\)

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