SOLUTION: ncr +2×ncr-1+ncr-2 =n+2cr

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Question 1045421: ncr +2×ncr-1+ncr-2 =n+2cr
Found 2 solutions by robertb, ikleyn:
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
To prove: .

We make use of the Pascal's Triangle: .
===>
=
=
= %28matrix%282%2C1%2Cn%2B1%2Cr%29%29+%2B+%28matrix%282%2C1%2Cn%2B1%2Cr-1%29%29,
= %28matrix%282%2C1%2Cn%2B2%2Cr%29%29

Answer by ikleyn(52781) About Me  (Show Source):
You can put this solution on YOUR website!
.
On Pascal's triangle see the lesson
    - The Pascal's triangle
in this site.