[tex] \bf \cfrac{(a-3)\left( \frac{a}{3}+1 \right)}{\frac{1}{3}}\implies 3\left[ (a-3)\left( \frac{a}{3}+1 \right) \right]
\\\\\\
3\left[\frac{a^2}{3}+a-a-3 \right]\implies 3\left[\frac{a^2}{3}-3 \right]\implies a^2-9 [/tex]
when you have polynomials multiplication, say (x+y) (a+b+c), you can always just multiply x(a+b+c) + y(a+b+c), namely each term by all others and sum them up, like above.
