Jika f (x) = x + 1 maka f (x2) - 2f (x) =

[tex]f( {x}^{2} ) = {x}^{2} + 1[/tex]
sehingga
[tex]f( {x}^{2}) - 2f(x) = (x {}^{2} + 1) - 2(x + 1) = {x}^{2} + 1 - 2x - 2 = {x}^{2} - 2x - 1[/tex]