C(7,2) is represents the number of ways of choosing 2 elements from a set that has 7 elements.
The general formula for `C(n r) = (n!)/(r!(n - r)!)`
`C(7, 2) = (7!)/(2!(7-2)!)`
=> `(7!)/(2!*5!)`
=> `(7*6)/2 `
=> 7*3
=> 21
The value of C(7, 2) = 21
Math