SOLUTION: Please help: (1)Use the binomial theorem to find the 18th term in the binomial expansion of [2m-n(sqrt(2)]^27 (2)Find the 69th number in the 72nd row (n=72) of Pascal’s triangle

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Question 936889: Please help:
(1)Use the binomial theorem to find the 18th term in the binomial expansion of [2m-n(sqrt(2)]^27
(2)Find the 69th number in the 72nd row (n=72) of Pascal’s triangle

Found 2 solutions by Edwin McCravy, AnlytcPhil:
Answer by Edwin McCravy(20056) About Me  (Show Source):
You can put this solution on YOUR website!

Your solution is below.  

Edwin McCravy aka AnlytcPhil


Answer by AnlytcPhil(1806) About Me  (Show Source):
You can put this solution on YOUR website!
(1)Use the binomial theorem to find the 18th term in the binomial expansion of [2m-n(sqrt(2)]^27
%282m%5E%22%22-n%2Asqrt%282%29%29%5E27

Usually the letter n is used to represent a general number, not a specific
number, but here n is used as a specific number, so I can't speak of the "nth
term", so I'll have to speak of the "pth" term instead to avoid conflict of
letters.

The pth term of %28q%2Br%29%5Es, if you start counting with 0 instead of 1, is

%28matrix%282%2C1%2Cs%2Cp%29%29q%5E%28s-p%29%2Ar%5Ep, 

where %28matrix%282%2C1%2Cs%2Cp%29%29 is the binomial coefficient which is the same as
C(s,p) or sCp or "the number of combinations of s things taken p at a time."

The 18th term is the 17th term if we start counting from 0, so we
substitute  

p=17, q=2m, r=-n%2Asqrt%282%29, s=27

into

%28matrix%282%2C1%2Cs%2Cp%29%29q%5E%28s-p%29%2Ar%5Ep

%28matrix%282%2C1%2C27%2C17%29%29%2A%282m%29%5E%2827-17%29%2A%28-n%2Asqrt%282%29%29%5E17 and simplify a little:

%28matrix%282%2C1%2C27%2C17%29%29%2A%282m%29%5E10%2A%28-n%29%5E17%2A%28sqrt%282%29%29%5E17

Further simplifying the factors separately:
   %28matrix%282%2C1%2C27%2C17%29%29 = 8436285 <-- using a TI-84 calculator
   %282m%29%5E10 = 2%5E10%2Am%5E10 = 1024m%5E10
   %28-n%29%5E17 = -n%5E17
   %28sqrt%282%29%29%5E17 = %28sqrt%282%29%29%5E%2816%2B1%29 = %28sqrt%282%29%29%5E16%2A%28sqrt%282%29%29%5E1 = %28sqrt%282%29%29%5E%282%2A8%29%2Asqrt%282%29 = %28%28sqrt%282%29%5E%22%22%29%5E2%29%5E8%2Asqrt%282%29 = 2%5E8%2Asqrt%282%29 = 256sqrt%282%29

Putting them all together:

8436285%2A1024m%5E10%2A%28-n%5E17%29%2A256sqrt%282%29

-2211521495040m%5E10n%5E17  <-- answer

------------------------------------

(2)Find the 69th number in the 72nd row (n=72) of Pascal’s triangle.
Again we start counting from 0, so the 69th number starting counting with 1,
is the 68th number, when we start counting with 0 instead of 1. 

%28matrix%282%2C1%2C72%2C68%29%29%22%22=%22%22%22C%2872%2C68%29%22%22%22=%22%221028790

If you can't use a calculator you can use 

%28matrix%282%2C1%2C72%2C68%29%29%22%22=%22%22%28matrix%282%2C1%2C72%2C72-68%29%29%22%22=%22%22%28matrix%282%2C1%2C72%2C4%29%29%22%22=%22%22%2872%2A71%2A70%2A69%29%2F%284%2A3%2A2%2A1%29%22%22=%22%221028790.

1028790  <-- answer

Edwin