Math Problem Statement
Which of the following is true?
A. The tenth term of the sequence 4, 7, 10, 13, … is 30.
B. an = 11 + 6n and an={11,if n=1an−1+6n,if n>1
both define the same sequence. C. The sum of the first 12 terms of the arithmetic series with a1 = −5 and a12 = 232 is 39. D. ∑20i=1(3i−15)=450
Solution
Let's analyze each statement one by one:
A. The tenth term of the sequence 4, 7, 10, 13, … is 30.
This is an arithmetic sequence where the first term and the common difference . The formula for the nth term of an arithmetic sequence is:
For , we have:
So, the tenth term is 31, not 30. A is false.
**B. and (a_n = \begin{cases}
11 & \text{if } n = 1 \ a_{n-1} + 6n & \text{if } n > 1 \end{cases}) both define the same sequence.**
Let's compare both definitions.
-
For :
For :
For :
For : -
For the recursive sequence (a_n = \begin{cases} 11 & \text{if } n = 1 \ a_{n-1} + 6n & \text{if } n > 1 \end{cases}):
For :
For :
For :
Clearly, the sequences are different. So, B is false.
C. The sum of the first 12 terms of the arithmetic series with and is 39.
The formula for the sum of the first terms of an arithmetic series is:
For , , and :
The sum is 1362, not 39. So, C is false.
D.
The sum can be rewritten as:
The sum of the first 20 terms of is:
The sum of repeated 20 times is:
Now, subtract:
So, the sum is 330, not 450. D is false.
Conclusion:
All four statements are false.
Do you want further details or have any questions?
Here are 5 related questions to explore:
- How do you find the sum of an arithmetic sequence?
- What is the difference between an explicit and recursive formula for sequences?
- How do you calculate the nth term of an arithmetic sequence?
- How can you decompose summations like ?
- How do you identify if two sequences are equivalent?
Tip: When working with summations, break them into simpler parts to handle constants and linear terms separately.
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Math Problem Analysis
Mathematical Concepts
Arithmetic Sequences
Recursive Sequences
Summation
Arithmetic Series
Formulas
nth term of an arithmetic sequence: an = a1 + (n - 1)d
Sum of an arithmetic series: Sn = n/2(a1 + an)
Summation of linear terms: ∑i=1n(ai + b) = a∑i=1ni + b·n
Theorems
Arithmetic sequence formula
Summation of an arithmetic series
Suitable Grade Level
Grades 10-12
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