Observe the following three lines: - 3, 9, - 27, 81, - 243 -5,7,-29,79,-245,… -1,3,-9,27,-81… (1) What is the order of the first row? (2) What is the relationship between the number of the second and third rows and the number of the first row? (3) Take the 10th number of the three rows and calculate the sum of the three numbers

Observe the following three lines: - 3, 9, - 27, 81, - 243 -5,7,-29,79,-245,… -1,3,-9,27,-81… (1) What is the order of the first row? (2) What is the relationship between the number of the second and third rows and the number of the first row? (3) Take the 10th number of the three rows and calculate the sum of the three numbers

(1)-3=(-1)131,9=(-1)232,-27=(-1)333,81=(-1)434,… So the n-th term is (- 1) n3n; (2) the number of the second row and each corresponding number of the first row plus - 2, the n-th term is (- 1) n3n-2; the number of the third row and each corresponding number of the first row multiplied by 13, the n-th term is (- 1) n3n-1; (3) the 10th number of the first row is (- 1) 10310 = 310; the 10th number of the second row is (- 1) 10310-2 = 310-2; the 10th number of the first row is (- 1) 10310-2 = 310-2 The sum of these three numbers is 310 + 310-2 + 39 = 7 × 39-2