If $2^{x-1}=(1/8{)}^{x+1}$, then $x$ equals:

Write the right side to base 2: 1/8 = 2⁻³, so $(1/8{)}^{x+1}=2^{-3x-3}$. Equating the indices gives $x-1=-3x-3$, hence $4x=-2$ and $x=-1/2$. Dropping the minus sign on the −3 gives the wrong value 2.