Find the number of the line and column where the number 2015 stays.
A number or a short expression. Spacing and $ signs are ignored.
Solution
We will analyze the pattern in the table to determine where the number 2015 is located. The arrangement of numbers in the table has a specific formulation in terms of line and column indices. We will first observe the pattern, derive the general formula for numbers at position (i,j), and then use it to find the location of the number 2015.
1. Pattern Observation:
Looking at the first few values: - First row: 1,3,6,10,15,… (These are triangular numbers: Tn=2n(n+1)) - First column: 1,2,4,7,11,16,… (These numbers follow a pattern where the difference between terms increases by 1: (2−1),(4−2),(7−4),…)
2. Row Analysis:
The j-th number in the first row is the j-th triangular number: Tj=2j(j+1).
3. Column Analysis:
The i-th number in the first column is the sum of the first i−1 natural numbers plus 1: Si=1+k=1∑i−1k=1+2(i−1)i.
4. General Formula:
For a number in the table located at position (i,j), the formula is: ai,j=Si+Tj−1. Simplified, this is: ai,j=1+2(i−1)i+2(j−1)j.
5. **Solving for 2015**:
We need to find i and j such that: 1+2(i−1)i+2(j−1)j=2015.
6. Approximations:
Start by trying values for i: - For i=62: S62=1+2(62−1)⋅62=1+261⋅62=1892. - Now solve: 1892+Tj−1=2015⇒Tj−1=2015−1892=123. - Find j: 2(j−1)j=123⇒(j−1)j=246. - Solving j2−j−246=0 using the quadratic formula yields: j=21+1+4⋅246=21+985=21+31=16 However, this solution for (j−1)=15; thus, j=2.
7. Conclusion:
The number 2015 is located in line 62 and column 2 of the table. Therefore, the answer is:
(62,2)
This approach successfully determines the correct position of the number 2015 in the table.
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Source: Omni-MATH,
licensed Apache-2.0.
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