3. If one root of the quadratic equation 3y2 – ky + 8 = 0 is 2/3, then find the value of k.
Sol. 3y2 – ky + 8 = 0
y = 2/3, is the root of given quadratic equation.
So it satisfies the given equation.
∴ 3(2/3)2 – k(2/3) + 8 = 0
∴ 3(4/9) – 2k/3 + 8 =0
∴ 12/9 – 2k/ 3 + 8 = 0
Multiplying the equation by 9 we get,
12 – 6k + 72 = 0
∴ 6k = 84
∴ k = 84/6
∴ k = 14