NDA 2018 Maths · Mathematics · Quadratic Equations · medium

If one root of x^2-9x+k=0 is twice the other, what is the value of k?

Single correct option

If one root of

x^2-9x+k=0

is twice the other, what is the value of

k

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Answer: (A) 18

Let the roots be

\beta

and

2\beta

. Sum

3\beta=9

gives

\beta=3

, roots 3 and 6, and

k=

product

=18

. Using the sum as

2\beta

or product as

2\beta

alone leads to the distractors.

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