Bài $1$.
$a$) $a^5 : a = a^{5-1} = a^4$.
$b$) $2^{13} : 2^2 = 2^{13-2} = 2^{11}$.
Bài $2$.
$a$) $11^3 : 11^2 = 1331 : 121 = 11$.
$11^3 : 11^2 = 11^{3-2} = 11^1 = 11$.
$b$) $16^2 : 4^2 = 256 : 16 = 16$.
$16^2 : 4^2 = (4^2)^2 : 4^2 = 4^4 : 4^2 = 4^{4-2} = 4^2 = 16$.
Bài $3$.
$a$) $(2n+1).3=27$
$⇔ 2n+1 = 9$
$⇔ 2n = 8$
$⇔ n = 4$
Vậy $n=4$.
$c$) $(2n-2).2 = (n-2).4$
$⇔ 4n - 4 = 4n - 8$
$⇔ 4n - 4n = -8 + 4$
$⇔ 0 = -4$ (Vô lý)
Vậy $n$ $∈$ $\varnothing$.