(Q9)Find the values of k for each of the following quadratic equations so that they have two equal roots.

(i)2x2 + kx + 3 = 0   (ii) kx(x-2) + 6 = 0

Answer

(i)Given: 2x2 + kx + 3 = 0 has equal roots

∴ b2 - 4ac = 0

Here a = 2; b = k; c = 3

b2 - 4ac

= (k)2 - 4()()

k2 - = 0

k2 =

k = √

k = ±2√

(ii) kx(x-2) + 6 = 0

kx2 - 2kx + 6 = 0

As this quadratic equation has equal roots,

b2 - 4ac = 0

Here

a = k; b = -2k; c = 6

∴ b2 - 4ac

= (-2k)2 - 4(k)() = 0

4k2 - k = 0

4k(k-) = 0

4k = 0 (or) k - = 0

k = 0 (or)

But k = 0 is trivial

∴ k=.