дано f(x)=x^-0,75.....Найдите f(81)

f(x)=x^(-0,75)
f(81)=?
f(81)=81^(-0,75)=81^(-75/100)=81^((-25×3)/(25×4))=81^(-3/4)=3^(4×(-3/4))=3^(-3)=1/3^3=1/27=0,03703704

f(81)=81^(-0,75)=(1/27)=0,03703704