Math Problem Statement

Consider a finite arithmetic sequence of positive integers. Among its terms are the numbers 28, 52 and 82. The sum of all terms in the sequence is 1769. Find the smallest and largest terms in the sequence. d=3

Solution

To solve this problem, let's consider the given finite arithmetic sequence. The sequence has a common difference d=3d = 3, and it contains the terms 28, 52, and 82. We are also given that the sum of all terms in the sequence is 1769.

Step 1: General Form of the Arithmetic Sequence

The general term of the arithmetic sequence can be written as: an=a1+(n1)da_n = a_1 + (n-1) \cdot d where a1a_1 is the first term, d=3d = 3 is the common difference, and nn is the position of the term in the sequence.

Step 2: Express the Known Terms

We are given that 28, 52, and 82 are terms in the sequence. Let ai=28a_i = 28, aj=52a_j = 52, and ak=82a_k = 82 for some integers i,j,i, j, and kk. Then we can express these terms as: 28=a1+(i1)328 = a_1 + (i-1) \cdot 3 52=a1+(j1)352 = a_1 + (j-1) \cdot 3 82=a1+(k1)382 = a_1 + (k-1) \cdot 3

Step 3: Solve for the Differences Between Indices

Subtract the first equation from the second: [ 52 - 28 = [a_1 + (j-1) \cdot 3] - [a_1 + (i-1) \cdot 3] ] 24=3(ji)24 = 3(j - i) ji=8j - i = 8

Now subtract the second equation from the third: [ 82 - 52 = [a_1 + (k-1) \cdot 3] - [a_1 + (j-1) \cdot 3] ] 30=3(kj)30 = 3(k - j) kj=10k - j = 10

So, we have j=i+8j = i + 8 and k=j+10=i+18k = j + 10 = i + 18.

Step 4: Write the Terms Using ii

Now, we can express the positions of these terms in terms of ii: ai=28,ai+8=52,ai+18=82a_i = 28, \quad a_{i+8} = 52, \quad a_{i+18} = 82

Step 5: Sum of the Sequence

The sum of all terms in the sequence is given by: S=n2(a1+an)S = \frac{n}{2} \cdot (a_1 + a_n) where nn is the total number of terms. We are given S=1769S = 1769.

Step 6: Calculate the First Term a1a_1

Since ai=28a_i = 28, we can express a1a_1 as: 28=a1+(i1)3soa1=283(i1)28 = a_1 + (i-1) \cdot 3 \quad \text{so} \quad a_1 = 28 - 3(i-1) Substituting into the other terms: 52=28+38=28+24=52(this checks out)52 = 28 + 3 \cdot 8 = 28 + 24 = 52 \quad \text{(this checks out)} 82=28+318=28+54=82(this checks out)82 = 28 + 3 \cdot 18 = 28 + 54 = 82 \quad \text{(this checks out)}

Step 7: Determine the Smallest and Largest Terms

To find the smallest and largest terms, note that the sequence starts at a1a_1 and ends at ana_n. The largest term is an=a1+(n1)3a_n = a_1 + (n-1) \cdot 3.

Given S=1769S = 1769: n2(a1+an)=1769\frac{n}{2} \cdot (a_1 + a_n) = 1769

Since we already have the three terms that fit in, the sequence should contain n=19n = 19 terms (based on ii and kk). The smallest term will be a1a_1 and the largest term a19a_{19}. We find:

a1=283(i1)anda19=a1+54a_1 = 28 - 3(i-1) \quad \text{and} \quad a_{19} = a_1 + 54

Thus, the sequence starts at 10 (smallest term) and ends at 82 (largest term).

Final Answer:

The smallest term is 10\boxed{10} and the largest term is 100\boxed{100}.

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Math Problem Analysis

Mathematical Concepts

Arithmetic Sequences
Sum of Arithmetic Series

Formulas

General term of an arithmetic sequence
Sum of an arithmetic series

Theorems

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Suitable Grade Level

Grades 9-12