Question

Which of the following is not a factor of

x4 – 4abx2 – (a2 – b2)

2?

Answer 1

x2+(a+b)2

let a=1,b=1
x4-4×1×1×x2-((1)2-(1)2)
x4-4x2-0

after expanding it answer is not 0
so,x2+(a+b)2 is not a factor