Question

как найти f(1\x) при f(x) = (x - 9\x) ?

Answer 1

$f(x)=x-\frac{9}{x} \; \; \Rightarrow \; \; \; f(t)=t-\frac{9}{t}\\\\t=\frac{1}{x}\; \; \Rightarrow \; \; \; f(\frac{1}{x})=\frac{1}{x}-\frac{9}{\frac{1}{x}}=\frac{1}{x}-9x$