Find the value of k , if one of the two roots of the equation : x2 + k X – 98 = 0 is double the additive inverse of the other.
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Given:

One of the two roots of the given equation is double  the additive inverse of the other.

To find:

The value of k.

Solution:

Let two roots of the given equation are and .

According to the question,

       (Additive inverse of is )

If and are roots of the quadratic equation then

We have,

Here, a =1, b=k and c=-98.

          ...(i)

Now,

Divide both sides by -2.

Taking square root on both sides.

Using (i), we get

Therefore, the value of k is either -1 or 1.