Consider f(x)=5x8\displaystyle {f{{\left({x}\right)}}}={5}{x}-{8}

f(2)=\displaystyle {f{{\left(-{2}\right)}}}=  

f(6)=\displaystyle {f{{\left({6}\right)}}}=  

f(s)=\displaystyle {f{{\left({s}\right)}}}=  

f(st)=\displaystyle {f{{\left({s}-{t}\right)}}}=