Here is a set of Coprime numbers: 6 and 9; 8 and 9; 12 and 21; 28 and 32

Here is a set of Coprime numbers: 6 and 9; 8 and 9; 12 and 21; 28 and 32

Definition and theorem 1. Two non-zero natural numbers with only 1 common factor of two numbers are called coprime numbers. Examples: 2 and 3, with only 1 common factor, are coprime numbers

From the 10 numbers of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10,
How many different products can you get by multiplying the sum of any five numbers by the sum of the other five numbers?

The smallest sum = 1 + 2 + 3 + 4 + 5 = 15
The largest sum = 6 + 7 + 8 + 9 + 10 = 40
So there are a total of 40-15 + 1 = 26 different sums, from 15, 16,..., 40
A total of 13 pairs (15,40) (16,39),... (27,28)
There are 13 different products

The following two groups of numbers are regular: one, 2.4.6.8.10. Two, 2. - 6.12. - 20.30. - 42
What are the eighth of the two groups?
Write the nth number of the two groups of numbers (n is a positive integer, expressed by the formula containing n) respectively?
Find the sum of the nth number in the two groups (simplify the column)

1、 The eighth number is 16, the sum of the first n numbers of 2n is (2 + 2n) * n / 2 = n (n + 1) 2. The eighth number is - 72, the sum of the first n numbers of (- 1) ^ n + n (n + 1) if it is even, let n = 2K, then a group of two is - 4 (1 + 2 + 3 +. + k) = - 2K (K + 1) if it is odd, let n = 2K + 1, the first 2n numbers are the same

There are three numbers, their average is 19.6, of which two numbers are 42.8 and 3 / 4, and the third number is 19.6{

19.6*3-42.8-0.75=15.25