open test...

Today's Question of Open test(FIITJEE AITS)

Let f(x) be a polynomial function of degree 4 satisfying..

(1∫xA(t)B(t)dt)(1∫xC(t)D(t)dt)-(1∫xA(t)C(t)dt)(1∫xB(t)D(t)dt)=f(x)

where A(x) B(x) C(x) D(x) are non constant continuous and differentiable function. Its is given that the leading coefficient(coefficient of x4) of f(x) is 1..

Q. Find f(x)

[7]

25 Answers

21
tapanmast Vora ·

wat approach did u use 4 this one?

repeated lebnitz??? but then vo ∫ kaise gaya?????/

9
Celestine preetham ·

thanks prophet sir
that q turned out to be a easy q made to appear difficult in the aits exam conditions ;)

24
eureka123 ·

try here,...http://www.math.niu.edu/~rusin/problems-math/[1][1]

341
Hari Shankar ·

and putnam is an a college level competition in the US. Its quite a prestigious one and this qn was asked in one of them. I will search for the solution and post it if its more illumining

341
Hari Shankar ·

Celestine asked how many numbers between 1 and 2000 are such that the sum of the digits of their square is 21.

The sum of the digits of the square is 21 means that we have a square that is divisible by 3 and not by 9. which is absurd. So, no such integers exist

341
Hari Shankar ·

Sorry, I wasnt watching this thread.

But celestine has already given the solution.

The idea is this: suppose you want to prove that (x-a)k divides f(x), then one possible approach is to prove that a is a root of f(x) repeated k times. in other words f(a) = f'(a) = f"(a) =..= fk-1(a) = 0.

Here if the integrals are p,q,r and s , then we have to prove that

for f(x) = ps-qr, we have f(1) = f'(1) = f"(1) = f"'(1) = 0

We have to note that p(1) = q(1) = r(1) = s(1) = 0

So f(1) = 0. f'(1) = (p's + ps' - qr' - q'r) at x = 1 and this again zero.

f'(1) = p's' - q'r' = 2( ABCD-ACBD) = 0

and so on ...(I havent gone further. But it will all turn out well :D)

33
Abhishek Priyam ·

abhi tak mere se nahi bana [2] [7] [12]

1
mithun ·

getting f'(x)=0.........anyone clarify how 4 degree polynomial ...prophet sir...

21
tapanmast Vora ·

cele,
didnt get ur questn dude ??? [7]

can u post it in a diff post with the entire questn....

jus chk i gues thers sumthin missin in da abov que as the 2 limits r only not given [2]...

33
Abhishek Priyam ·

none of these. .:p

9
Celestine preetham ·

guys did ne one get how to do the sum of digits of a sqr q ?

pls help

Q how many nos btw 1,2000 exist such that the sum of the digits of its sqr is 21.

21
tapanmast Vora ·

hmmmm.... yeah got it...

nice soln.....

9
Celestine preetham ·

that is only x-1^4 nihit

1
Philip Calvert ·

[11][11]what a question !!
plz give a bit of ffree air to - it will suffocate to non existence [4]
i had to glare to find it

21
tapanmast Vora ·

hi nihit......

so did u get da ans in dat optics que???

did u get my message??????

3
nihit.desai ·

hey will it be x^4 - 4x^3 + 6x^2 - 4x +1 ??

9
Celestine preetham ·

if u diff it repeatedly ull get

f1,f'1,f''1,f'''1 =0 so f is x-1^4

1
Philip Calvert ·

i didn't see he was online that time
well now here we are in wait of a solution from prophet sir
"i am quite sure, prophet will have a solution... "
if he hasn't he will find one and it will be an interesting one too..

21
tapanmast Vora ·

an old putnam problem rehashed iska kya matlab hai???????????/

1
skygirl ·

philip, i am quite sure, prophet will have a solution...

i am very sure [1]

33
Abhishek Priyam ·

are soln nahi hai bas isitarah hai..

"given soln:

Since f(x) is divisible by (x-1)4 so f(x) is (x-1)4
"

341
Hari Shankar ·

an old putnam problem rehashed

1
Philip Calvert ·

you can rest assured no one here (at least the likes of me) are going to try it
so you can post the soln right away abhi

1
skygirl ·

[3]

nahi kiye...

dekh kar hi chhor diye [3]

33
Abhishek Priyam ·

Soln dekhkar to aur bada :0

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