fft1 p1 10

MULTIPLE ANSWER QUESTION

If f(x) = 0 is a polynomial whose coefficents are all ± 1 and whose roots are all real, then degree of f(x) can be equal to

(A) 1 (B) 2 (C) 3 (D) 4

17 Answers

4
UTTARA ·

EDITTED

4
UTTARA ·

ya right Sorry .....[3] So stupid of me

1
rahul nair ·

constant is nothing but co-efficient of 'x^{0}' in the polynomial....which i think u hav to take ±1
(Hope i m not talkink any blunder [3])

4
UTTARA ·

I think there need not b a constant term becz the qs said coefficients shud be +- 1 & nothing is mentioned abt constant term

its like this

if v say an eqn has all positive coeffs then it need not be that constant term shud also be positive no???

1
rahul nair ·

ya..in a general polynomial, there should be a constant term ......................which u have taken as '0'..
but qs says it should be ±1

4
UTTARA ·

@Rahul (#12 )

The qs mentions that the coefficients shud be ± 1

So it is not necessary that the constant term is also ±1 na ??

@msp : I too thought the same way

@ Asish : Ya u're ans is correct

but my doubt is shud there be a constant term at all ??

3
msp ·

i thot we shud also include repeated roots

y=x2(x2-1)=x4-x2.

106
Asish Mahapatra ·

is there any mathematical proof for this??

yeah ans should be ABC

1
rahul nair ·

but u have taken the constant term in the above eqn as 0,
but ques says that every term should be +1 or -1

24
eureka123 ·

a,c ??

29
govind ·

the eqn that u have posted can be written as x4 - 2x2 + x = 0...which do not satisfy the condition given abv...

4
UTTARA ·

(x2 + x)(x2 - 1) = 0

1
rahul nair ·

Uttara can u show how four??

Acc. to me, A,B,C should be right.........

29
govind ·

oops i misread the question ..i thought both roots and coefficients have to be ± 1 [13]

4
UTTARA ·

Ya Rahul It can also be 2

In fact I was getting A B C D

But ans given is A B C

I say it can also be 4 ( Considering repeated roots)

1
rahul nair ·

x2+x-1=0 also has real roots

so why cant it be 2?

29
govind ·

ya i also feel the answer shud be A and C...
logic : number of terms shud be even so that they can be cancelled out...

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