CONCEPT: Roots of a quadratic equation satisfy the equation, so by putting the value of one root, One can find the unknown variable and hence the other root. CALCULATION: Let us put x = 3 in the equation x2 – 12x + k = 0, ⇒ 9 – 36 + k = 0 ⇒ k = 27 Putting the value of k in the equation, we get: x2 – 12x + 27 = 0 ⇒ x2 – 9x – 3x + 27 = 0 ⇒ x(x – 9) – 3 (x – 9) = 0 ⇒ (x – 3)(x – 9) = 0 ⇒ x = 3 and 9 ∴ Other root of the equation is 9