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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