A5. What is $a$, if the equation $x^{2}=3(a x-3)$ has exactly one real solution?
(A) $a=2$ or $a=-2$
(B) $a$ can only be 2
(C) $a=4$
(D) $a=6$ or $a=-6$
(E) $a=\frac{2}{3}$
A5. The equation is transformed into $x^{2}-3 a x+9=0$. Its discriminant is $D=9 a^{2}-36$ and is equal to zero if $a=2$ or $a=-2$.