Observe the following three lines: 0, 3, 8, 15, 24 ①2，5，10，17，26，… ②0，6，16，30，48，… ③ (1) what is the rule of the number of the first line? (2) What is the relationship between the number of rows 2 and 3 and the number of rows 1? (3) Take the seventh number in each row and find the sum of the three numbers

Observe the following three lines: 0, 3, 8, 15, 24 ①2，5，10，17，26，… ②0，6，16，30，48，… ③ (1) what is the rule of the number of the first line? (2) What is the relationship between the number of rows 2 and 3 and the number of rows 1? (3) Take the seventh number in each row and find the sum of the three numbers

(1) ∵ 0 = 12-1, 3 = 22-1, 8 = 32-1, 15 = 42-1, 24 = 52-1, the nth number is n2-1; (2) the number of the second row is 2 larger than that of the first row, so the nth number of the second row is N2 + 1; the number of the third row is 2 times of that of the first row, so the nth number of the third row is 2n2-2; (3) three

Minus five times bracket minus eleven fifths bracket plus thirteen times bracket minus eleven fifths bracket minus three times bracket minus eleven fifths bracket

–11

Several simple mathematical problems
5.3+2.55/1.7
（70+0.42）/7
4.2/28

5.3+2.55/1.7=5.3+1.5=6.8
(70+0.42)/7=70.42/7=10.06
4.2/28=0.15