7. (8th grade) For what values of $x$ is the polynomial $x^{4}+2 x^{3}-2 x^{2}-$ $-4 x-5$ a perfect square?
7. Let's complete the square $\left(x^{2}+x-2\right)^{2}+x^{2}-9$. The polynomial will be a perfect square if $x^{2}-9=0$, i.e., when $x= \pm 3$.