5. If one root of the quadratic equation kx2 – 7x + 12 = 0 is 3, then find the value of k.
Sol. kx2 – 7x + 12 = 0
x = 3 is root of given quadratic equation.
So it satisfies the given equation
∴ k(3)2 – 7(3) + 12 = 0
∴ k(9) – 21 + 12 = 0
∴ 9k – 9 = 0
∴ 9k = 9
∴ k = 9/9
∴ k = 1