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If one zero of the polynomial f(x)=(k² + 4)x² + 13x + 4k is reciprocal of the other zero, then value of k is :
Question

If one zero of the polynomial f(x)=(k² + 4)x² + 13x + 4k is reciprocal of the other zero, then value of k is :

A.

-2

B.

-1

C.

2

D.

1

Correct option is C

Solution:


Given:

The polynomial is f(x) = (k2+4)x2+13x+4k(k^2 + 4)x^2 + 13x + 4k​ . One zero of the polynomial is the reciprocal of the other.

Condition for Reciprocal Roots:

If one root is the reciprocal of the other, the product of the roots is:

Product of roots=1\text{Product of roots} = 1​​


For a quadratic polynomial ax2+bx+cax^2 + bx + c​ , the product of the roots is:

Product of roots=ca\text{Product of roots} = \frac{c}{a}​​


Coefficients of the Polynomial:

Coefficient of x2:a=k2+4x^2 : a = k^2 + 4
 Constant term: c = 4k

Substitute these values into the condition:

ca=1\frac{c}{a} = 1​​


Solve for k :


4kk2+4=1\frac{4k}{k^2 + 4} = 1​​

Multiply through by k2k^2​ + 4 (assuming k2+40k^2 + 4 \neq 0​ ):

4k = k2k^2​ + 4

Rearrange:

k2k^2​ - 4k + 4 = 0

Factorize:

(k2)2(k - 2)^2 ​= 0

Solve:

k = 2


Final Answer:

Option C: 2

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