tolong ya nomor 4 beserta caranya

Misal :
b - a = n
a - b = -n

1/(1 + x^(b - a)) + 1/(1 + x^(a - b))
= 1/(1 + x^n) + 1/(1 + x^-n)
= 1/(1 + x^n) + 1/(1 + x^-n) . (x^n)/(x^n)
= 1/(1 + x^n) + (x^n)/(x^n + 1)
= (1 + x^n)/(1 + x^n)
= 1