Step-by-step explanation:
(a^b)^c = a^(b×c)
so,
(a^(-1))^(-1) = a^(‐1×-1) = a¹ = a
a^(-1) = 1/a
(a^(-1))^(-1) = 1 / 1/a = 1/1 / 1/a = (a×1)/(1×1) = a