a, $\dfrac{2.14}{7.8}$
$= \dfrac{2^2.7}{2^3.7}$
$=\dfrac{1}{2}$
b, $\dfrac{3.7.11}{22.9}$
$=\dfrac{3.7.11}{2.3^2.11}$
$=\dfrac{7}{2.3}=\dfrac{7}{6}$
c, (không rút gọn được)
d, $\dfrac{ax+ay}{bx+by}$ ($x\neq -y$, $b\neq 0$)
$=\dfrac{a(x+y)}{b(x+y)}$
$=\dfrac{a}{b}$
e, $\dfrac{8a-8t}{(a-t)(a-t)}$ ($a\neq t$)
$=\dfrac{8(a-t)}{(a-t)(a-t)}$
$=\dfrac{8}{a-t}$
f, $\dfrac{2m+2n}{(m+n)(m-n)}$ ($m\neq \pm n$)
$=\dfrac{2(m+n)}{(m+n)(m-n)}$
$=\dfrac{2}{m-n}$