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 #2
avatar+201 
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May 19, 2021
 #3
avatar+118653 
+1

A polynomial with integer coefficients is of the form

 \(2x^4 + a_3 x^3 + a_2 x^2 + a_1 x + 1 = 0.\)
Find the number of different possible rational roots of this polynomial.

 

I just found this         HERE

 

The rational root test theorem says that, if rational factors of a polynomial exist, then they are always in the form of

                       ±(factor of last coefficient) / (factor of first coefficient)

 

So the rational roots could be     1, -1,   0.5,  -0.5   and that is it. 

It can't be all of those because the product of the roots must be +0.5  so it can't have 4 rational roots

It could definitely have no real roots, so therefore no rational roots.

 

 

So could it have 1 or 2 or 3  rational roots? 

It can have 3

2(x-1)(x+1)(x+0.5)(x-1)= 0   that works

 

I don't know about 1 or 2

I suspect it could have 2 but not 1, not sure though.

 

So it can't have 4 or more.   It could have 3 or 0.   

I don't think it can have 1 but I am not sure.  I can probably have 2.

 

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I  expect are theorem/s that would make this nice and easy ....

May 19, 2021

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