$\"\"$

The expression is $\"\"$ .

The number of combinations of n distinct objects taken r at a time given by $\"\"$ .

$\"\"$

$\"\"$ (Subtract: $\"\"$ )

Expand the factorial: $\"\"$ .

$\"\"$

$\"\"$ (Cancel common terms)

Multiply: $\"\"$ .

$\"\"$

$\"\"$ (Divide: $\"\"$ )

$\"\"$ (Multiply: $\"\"$ ) $\"\"$

The value of $\"\"$ is $\"\"$ .