pascal's triangle (subtraction)

[Guest]

hi,I was wondering how you do this:

Express as a single term from Pascal's triangle: t subscript (18,12) - t subscript (17, 12) The answer is t subscript (17, 11)

How do they get this?
thanks.

 

[pka]

If I were you, I would do a web search for Pascal's triangle.
There is just so much written on this.