How many pairs of Coprime are there in 4, 3, 7, 9?

How many pairs of Coprime are there in 4, 3, 7, 9?

three

Choice: 8.9.10.15 these four numbers constitute several pairs of Coprime numbers

Eight and nine, eight and fifteen, nine and ten, three pairs

The coprime numbers with "9" are as follows:_____________________________
If "and 9 have only one common divisor, the number of 1 is its coprime number! But with the exception of one, there are countless?

And 9 have only one common divisor. The number of 1 is its coprime number, except 1····

Mutual judgment
Why is positive integer n and 3N2 + 7n-1 coprime and how to prove it? (where 2 is square)

(3n²+7n-1)/n
=[3n²+6n+(n-1)]/n
=3n+6+(n-1)/n
n≠1
Then (n-1) and N are coprime, so (3N & sup2; + 7n-1) / N is a non integer
That is, positive integer n and 3N2 + 7n-1 are coprime