Tìm X biết

Tìm X:
a (x+$1/3{)}^2$ = 1/81
b. (2x$-3{)}^3$= -64
c. ${(-1/3)}^{\mathrm{x} }= 1/81$
$-512/343 = {(-8/7)}^{\mathrm{x}}$​d.