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Q.

Which of the subsequent is correct for the zeroes of the quadratic polynomial p(x)= x 2 +kx+k ,k0  ?


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a

They can’t be positive

b

They can’t be negative

c

They are always equal

d

They are always unequal 

answer is A.

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Detailed Solution

The given polynomial is,
p(x)= x 2 +kx+k ,k0  
α+β=k & αβ=k     If α and β   are the zeroes of a x 2 +bx+c ,   then
  α+β= b a  and αβ= c a   Since the given polynomial is,
p(x)= x 2 +kx+k ,k0  
α+β=k & αβ=k     The sum and product of two numbers will be positive if both numbers are positive.
Therefore α and β   can’t be positive, as if both are positive then sign of α+β   and αβ   will be positive but here clearly they are of opposite sign.
Therefore, they can’t be positive.
If k>0,   then both roots can be negative.
If the discriminant is zero, then we have,
k 2 4k=0 k=4   Since it is given that, k 0.   So both roots can be equal.
Also, it will have equal zeroes only if k=4.  
Therefore, they aren’t always unequal.
Thus, the zeroes of the quadratic polynomial p(x)= x 2 +kx+k ,k0    can’t be positive.
Hence, option (1) is correct.
 
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