The correct answer is option 1 i.e. a−xa+x.
(a3+x3(a+x)(ax2−x3)×a2x2+x4a2−ax+x2)÷(a4−x4)(a2−2ax+x2)(a−x)
⇒ ((a+x)(a2+x2−ax)(a+x)(ax2−x3)×x2(a2+x2)(a2−ax+x2))÷(a−x)(a+x)(a2+x2)(a−x)2(a−x)
⇒ x2(a2+x2)(ax2−x3)÷(a+x)(a2+x2)(a−x)2
⇒ x2(a2+x2)(ax2−x3)×(a−x)2(a+x)(a2+x2)
⇒ x2x2(a−x)×(a−x)2(a+x) = (a−x)(a+x)