Binomial Coefficients in Pascal's Triangle
Numbers written in any of the ways shown below. Each notation
is read aloud "n choose r".
These numbers, called binomial
coefficients because they are used in the binomial
theorem, refer to specific addresses in Pascal's
triangle.
They refer to the nth row, rth element
in Pascal's triangle as shown below.
The formula used to compute binomial
coefficients directly is found below as well.
Example: 
is
the 5th row, 4th element, so
_{5}C_{4} is
another notation for the same element. 
