If a differentiable function  $f\left(x\right)$ satisfy the following relation $f\left(x\right)+f\left(x^2\right)+f\left(x^3\right)=f(x+x^2+x^3)\forall x\in R,$
  then which of the following is 
INCORRECT?
 

$f\left(x\right)+f\left(x^2\right)+f\left(x^3\right)=f(x+x^2+x^3)$  differentiating w.r.t  $x$ we get
$f\text{'}\left(x\right)+2xf\text{'}\left(x^2\right)+3x^{2}f\text{'}\left(x^3\right)=(1+2x+3x^2)f\text{'}(x+x^2+x^3)$
Put  $x=1\Rightarrow 6f\text{'}\left(1\right)=6f\text{'}\left(3\right)\Rightarrow f\text{'}\left(1\right)=f\text{'}\left(3\right)$
Put  $x=-1\Rightarrow 4f\text{'}(-1)-2f\text{'}\left(1\right)=2f\text{'}(-1)\Rightarrow f\text{'}\left(1\right)=f\text{'}(-1)$
Put $x=1$  in given relation  $3f\left(1\right)=f\left(3\right)$
Put  $x=-1$ in given equation  $2f(-1)+f\left(1\right)=f(-1)\Rightarrow f(-1)+f\left(1\right)=0$