If 1x^2 + a^2 = x^2 - a^2, then the value of x is:

Answer: Option D

$$\begin{array}{rl}& \frac{1}{x^2+a^2}=x^2-a^2\\ & 1=x^4-a^4\\ & x^4=1+a^4\\ & x={\left(1+a^4\right)}^{\frac{1}{4}}\end{array}$$