Pascals Triangle: using it to solve 5(n_C_1) = (n + 1)_C_8

fencer817

New member
Joined
Dec 15, 2006
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13
Hmmm... I never learned this and its going to be on the final.

Solve for the value of n:

5(<sub>n</sub>C<sub>1</sub>) = <sub>n + 1</sub>C<sub>8</sub>
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Edited by stapel -- Reason for edit: formatting
 
To learn how to simplify "<sub>m</sub>C<sub>n</sub>" (pronounced as "emm, choose enn"), try reviewing lessons online covering combinations.

. . . . .Google results for "combinations"

After you've learned the notation and have set up the exercise's equation, if you get stuck solving it, please reply showing how far you have gotten. Thank you.

Eliz.
 
Ok i plugged in the four given answers and none of them worked. I also tried changing the equation around by dividing each side by five. Still nothing. The answers are


12, 7, 8, 9
 
Which is the question?
\(\displaystyle 5 {n \choose 1} = {{n+1} \choose 8}\) OR \(\displaystyle 5 {n \choose 1} = { n+ {n \choose 8}\)
 
Check again. One of your answers does indeed work.

Do you have a calculator?. One that does combinations?.

Let's check 12:

5*C(12,1)=60

C(13,8)=1287

Nope, not that one. 3 more to try. It's one of them.
 
8 isn't either

5*C(8,1) = C(9,8)

40=9

HA!!!
I calculated 9 wrong

5*C(9,1) = C(10,8)
45=45

sweet!
 
I agree that one of the given answers does in fact work!
BUT, how could this be worked without being given possible answers?
 
that is a good question. One that i do not know. I don't know how you divide Combinations.
 
Here, let's make it easy.

\(\displaystyle \L\\5C(n,1)-C((n+1),8)=0\)

\(\displaystyle \L\\\Rightarrow{\frac{-n^{8}}{40320}+\frac{n^{7}}{2016}-\frac{11n^{6}}{2880}+\frac{n^{5}}{72}-\frac{127n^{4}}{5760}+\frac{n^{3}}{288}+\frac{29n^{2}}{1120}+\frac{279n}{56}}=0\)

One of the roots of this is your answer. :D
 
Hmmm... what is that. I understand the part where you put all the parts of the equation on one side however what is the othe thing?
 
Yes, I came up with that too.
But that is an unreasonable question or equation to do.
Most CAS will have trouble with that one.
 
A Computer Algebra System is a program for doing symbolic mathematics.
 
I know, pka, that's why I put a smiley face there. Maple gave the answer quick, though.
 
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