ini gimana ya?? mohon bantuannya

[tex]\displaystyle f\left(x-\frac1x\right)=x^3-\frac1{x^3}\\f\left(x-\frac1x\right)=\left(x-\frac1{x}\right)\left(x^2+1+\frac1{x^2}\right)\\f\left(x-\frac1x\right)=\left(x-\frac1{x}\right)\left(x^2-2+\frac1{x^2}+3\right)\\f\left(x-\frac1x\right)=\left(x-\frac1{x}\right)\left(\left(x-\frac1{x}\right)^2+3\right)\\f(x)=x\left(x^2+3\right)\\\boxed{\boxed{f(x)=x^3+3x}}\\\\\\\text{gunakan rumus :}\\a^3-b^3=(a-b)(a^2-2ab+b^2)[/tex]