# Thread: 4 the maths lovers...??? help!!!

1. Originally Posted by zing
hullo?? n-1=48 => n=47 ???
i think n-1=48 => n=49
so by ur logic
49^2 - 49 -41 = 7
2401 - 49 - 41 = 7
2311 = 7
When we divide 2311 by 7, it gives 330.1428...

now what???

n math induction WONT work also cos we gotta prove its NOT divisble rite?

wht u do is:
suppose n^2 - n -41 IS divisble ...asumption
so n^2 - n - 41 = 7k [where k is a whole number 0,1,2,3...]
since this is true for all values of n, it must be true for n=0
0^2 - 0 - 41 = 7k
-41 = 7k
so k = -5.857... [NOT a whole number so our assumption is false]

just posting so tht mr singh dont get 'jhapped' tomoro in class hehe
Holy S.hit! Am I that dumb? Look guyz im sorry for all that B.ull S.hit (thanks Mr. Singh!) I'll try to get u some more acceptable solution for that. Jus gimme this night n a cuppa coffee. See ya tomorrow. Now I wonder how i got the right answer outta nowhere...... Have to work my brain cellz. Im outta here. Peace

2. Originally Posted by zing
nother way 2 look at it is
n^2 - n - 41 [write -n as -3n + 2n and -41 as -6-35]
n^2 - 3n + 2n - 6 -35
= (n-3)(n+2) -35 [since 35 is neway div by 7 so u can ignore it]
=> (n-3)(n+2) shd be div by 7

this is true wenever n-3 = 7,14,21,... or n+2 = 7,14,21,....

thas y it works when n=5 like u said ...

Now thats what they call nerd maths.... Though I still dont get the exemption of -35 from the equation....

3. And knight's gf, thanks for ur support. Its a pity it was in vain. N Mr. Singh said some abt ulams doodles n diagonals... its making some sense to me.... Hez right tht no formula can give a continuous sequence of prime no.s

4. => [BOLD](n-3)(n+2) shd be div by 7[/BOLD]

this is true wenever n-3 = 7,14,21,... or n+2 = 7,14,21,....

Excuse me Zing, but aint u making the same mistake as me????? Look close.

5. dude

6. Tabber
Join Date
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evo... dont worry, we all r a bit strange @ times.
the reason 4 the 35 being exempt/ excluded, is because ne multiple of a number minus another multiple of the same number will result in a multipl of same number... i.e. 7x40 - 7x3 is still a multiple of 7... i.e. 280 - 35 is still a multiple of seven. therefore if one of the preceding brackets is a multiple of 7, then by subracting 35, the answer will still remain a multiple of 7. this can b explained easier, as 7 is a common factor, and therefore, if ne of the brackets was 7, then the equation could be factorised one step further by extracting 7 from the brackets as the common term

7. righto. Now thats 1 simple solution in the whole thread! N thanks for the pm zing, it helped too.

8. Tabber
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thanks a lot zing... had maths 2day, u were rite... teacher had asked a trick question... idiot

9. waah!!!!waah!!!!

10. Tabber
Join Date
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Location
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the question ws meant 2 b an example of proof by contradiction, i think

11. No guyz, sorry. Busted my head open, 2 hrs of nothing but maths tricks n logics, but couldn't find anything to put together the right way. Its a fake

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