$p(x)=0$ with real coefficient has purely Imaginary roots.Then the equation $p(p(x)) = 0$ has If the Quadratic equation $p(x)=0$ with real coefficient has purely Imaginary roots.Then the 
equation $p(p(x)) = 0$ has 
$\bf{OPTIONS::}$
$(a)\;\; $ Only purely Inaginary Roots.  $\;\;\;\;\;\;(b)$ all real roots.
$(c)$ Two real and Two purely imaginary roots.$\;\;\;\;\;\;(d)$ neither real nor purely imaginary roots.
$\bf{My\; Try}::$ Let $p(x) = x^2+1.$ Then $p(p(x)) = (x^2+1)^2+1 = x^4+2x^2+2$.
Now Roots of $\displaystyle p(p(x))=0\Rightarrow x^4+2x^2+2=0\Rightarrow x^2 = \frac{-2\pm\sqrt{4-8}}{2} = \frac{-2\pm 2i}{2} = -1\pm i$
So $x^2=-1+i\;\;,-1-i$. Means $x$ must be in the form of $a+ib\;,$ where $a,b\neq 0$ and $i=\sqrt{-1}$
So option $(d)$ mut be Correct.
But my question is how can we solve the given question in Analytical method. means not by guessing.
Help me 
Thanks

If a quadratic equation has purely imaginary roots, then it can be written in the form $p(x)=k(x-ai)(x+ai)=k(x^2+a^2)$ for some $k,a\ne0$.
Hence $p(p(x))=k[k^2(x^2+a^2)^2+a^2]=k^3x^4+2k^3a^2x^2+k^3a^4+ka^2$.  By the quadratic equation, this gives us 
$$x^2=\frac{-2k^3a^2\pm\sqrt{4k^6a^4-4k^3(k^3a^4+ka^2)}}{2k^3}=\frac{-2k^3a^2\pm\sqrt{-4k^4a^2}}{2k^3}=\frac{-ka^2\pm ia}{k}$$
This means that $x$ can be neither purely real or purely imaginary, since if it were, then $x^2$ would be real.
