Did you find out? What is the relationship between the last number of each line and the line number?
(1) The number 12 in line 3 1 is the square of 30 plus 12, which is 912;
(2) Because the square of 44 is 1936 and the square of 45 is 2025,
So 1936 is the square number closest to 2007.
2007- 1936=7 1,
Therefore, 2007 is the 45th line, with the number 7 1.
Method 2:
Suppose * * * has n rows,
The number of 1 in line 1,
Number 3 in the second row,
Number five in the third row,
……
Number 2n-3 in line n- 1,
The number 2n- 1 in the nth row,
The total number of the first n- 1 rows is1+3+5+7+...+(2n-3) = (n-1) 2 (arithmetic progression sum).
* * * The total number is1+3+5+7+...+(2n-1) = n 2, (arithmetic progression sum).
The total number of * * * in the first 30 lines of (1) is 30 2 = 900, so the number of 12 in 3 1 line is 900+12 = 912;
(2) Because the square of 44 is 1936 and the square of 45 is 2025,
So 1936 is the square number closest to 2007.
2007- 1936=7 1,
Therefore, 2007 is the 45th line, with the number 7 1.