Question

x+4 / x-4 = a+b+4 / a+b-4

Answer 1

Use componendo and Dividendo
x + 4 + x - 4 a + b + 4 + a + b - 4
_________ = ______________
x + 4 - x + 4 a + b + 4 - a - b + 4

2x 2a + 2b
__ = _____
8 8

x = a + b