If you write it in the equation editor:$\frac{ 2^{1-x} }{ 4^{x-2} }$This is already more clear. Now remember that 4=2², so write it as:$\frac{ 2^{1-x} }{ (2^2)^{x-2} }$ Use these rules:$(a^b)^c=a^{bc}$and$\frac{ a^b }{ a^c }=a^{b-c}$to finish it off!