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mathematical induction (2 Viewers)

Riviet

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Someone from my class wrote a hilarious proof by induction that some particular student was always wrong (it was also an in-joke which made it all the funnier).
 

~shinigami~

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SoulSearcher said:
I have something exactly like that, name deleted for privacy reasons :eek:
This is gonna sound really dumb but I don't get it. :(

Riviet said:
Someone from my class wrote a hilarious proof by induction that some particular student was always wrong (it was also an in-joke which made it all the funnier).
Post it up Riviet, I wanna see. Math jokes are always so funny. :p
 

Riviet

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I can't remember it fully because it was written on the board quite a long while ago...

It went something like this:

Let S(w) be the statement that so and so is wrong.

Consider w=1, which is true since so and so was wrong in the first place.

[insert proof for k+1] etc...

Conclusion:

Therefore since so and so is wrong once, then he will be wrong again (w=2)
Since so and so is wrong twice, he will be wrong again (w=3)
Therefore it follows that so and so will always be wrong by mathematical induction.

:D
 

anniea89

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See, I can do MI, but the question in my prelim exam....I screwed up big time.
 

dlesmond

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Hi I have an induction question....

The pattern starts out 3+8+15+24+.....n(n+2) = [n(n+1)(2n+7)] / 6 (all over 6)

I got to the 2nd step of substituting k+1 for n but get stuck there

Any help would be great thanks....
 

airie

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So after proving the base case, if there exists a positive integer k such that the statement is true,

1(1+2)+2(2+2)+...+k(k+2)+(k+1)(k+3)
=[k(+1)(2k+7)]/6+(k+1)(k+3) [by inductive hypothesis]
=1/6*(k+1)[k(2k+7)+6(k+3)]
=1/6*(k+1)(2k^2+7k+6k+18)
=1/6*(k+1)(k+2)(2k+9)
={k*[(k+1)+1]*[2(k+1)+7]}/6
ie. k+1 satisfies the statement as well.

Therefore, by induction...
 

fishy89sg

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not to mention that mathematical induction is in our hsc course..
 

Riviet

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SoulSearcher said:
The questions that they give in the extension 1 HSC exam aren't really that difficult for induction most of the time.
I agree, they're generally straightforward without too much hassle if you know your work. However, that's a different story in extension 2 induction... :rolleyes:
 

~shinigami~

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Now I feel so dumb, I got stuck during Step 3 in my exam today. :p

It was a division one and I subbed in the thing from Step 2 then I was stuck...at least I'll get a few marks.
 

~shinigami~

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I can't remember what 3 was to the power of. Damn. :(

It was something like this though.

Prove by M.I that 72n + 3?? is divisible by 11.
 
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