[tex]f(x)=\dfrac{1}{x}\to y=\dfrac{1}{x}\\\\\text{exchange x with y and solve for y}\\\\x=\dfrac{1}{y}\\\\\dfrac{x}{1}=\dfrac{1}{y}\qquad|\text{cross multiply}\\\\xy=1\qquad|\text{divide both sides by x}\\\\y=\dfrac{1}{x}\\\\Answer:\ B)\ f^{-1}(x)=\dfrac{1}{x}[/tex]
