Q. 24.2( 234 Votes )

For what values of k, the roots of equation x2 + 4x + k = 0 are real?
Or

Find the value of k for which the roots of equation 3x2 – 10x + k = 0 are reciprocal of each other?

Answer :

For roots to be real D ≥ 0

⇒ b2 - 4ac ≥ 0
For x2 + 4x + k = 0, 

⇒ 42 - 4(1)k ≥ 0

16 – 4k ≥ 0

 – 4k ≥ - 16

4k ≤ 16

k ≤ 4

Or
Consider 3x2 – 10x + k = 0,
Compare the given equation with the general equation ax2 + bx + c = 0
So, a = 3, b = -10, c = k

Let, the roots of the equation be x and 1/x.

Product of the roots

k = 3

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