Find k, if one of the roots of the quadratic equation kx2 – 7x + 12 = 0 is 3.

3. Find k, if one of the roots of the quadratic equation kx² – 7x + 12 = 0 is 3.

Sol. kx² – 7x + 12 = 0

∵ 3 is one of the root of the quadratic equation, kx² – 7x + 12 = 0

∴  x = 3 satisfies the equation,

Substituting x = 3 in equation we get,

k (3)² – 7 (3) + 12 = 0

∴ 9k – 21 + 12 = 0

∴  9k – 9 = 0

∴  9k = 9

∴  k =  9/9

∴  k = 1