Question

If x = 3 is a solution of the equation $3x^2+(k-1)x+9=0,$ then k = ?
(a) 11
(b) −11
(c) 13
(d) −13

Answer 1

(b) −11
$$\begin{gathered} \mathrm{It}\mathrm{is}\mathrm{given}\mathrm{that}x=3\text{is a solution of 3}{x}^2+(k-1)x+9=0;\mathrm{therefore},\mathrm{we}\mathrm{have}: \\ 3{\left(3\right)}^2+\left(k-1\right)\times 3+9=0 \\ \Rightarrow 27+3(k-1)+9=0 \\ \Rightarrow 3(k-1)=-36 \\ \Rightarrow (k-1)=-12 \\ \Rightarrow k=-11 \end{gathered}$$