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
...............Многоточие
1)х^4-16х^2=(x^2)^2-(4)^2=(x^2-4x)(x^2+4x)
2) -4х^2-8ху-4у^2=-4(x^2+2xy+y^2)=-4(x+y)^2