When does a quadratic equation have identical roots?

Eqn can be written as $(2x\pm 3)^2$ +(k $\pm$ 12)x=0. Obviously for identical roots $k\pm12=0$ or k= $\pm12$ .But since k>0 $\Rightarrow \color{limegreen}{\boxed{ k=12}}$

A quadratic equation has identical roots if and only if the discriminant equals $0$

Discriminant of $4x^2+kx+9=k^2-4(4)(9) = k^2-144=0 \Rightarrow k^2=144 \Rightarrow k=\pm 12$

Hence , positive value of $\boxed{k=12}$ .

$ax^2+bx+c=0$
When equal roots $b^2-4ac=0$ .
$k^2-×4(9)×(4)=0$
$k^2=144$
$\therefore k=\boxed{12}$