Question

49c^2/(b-7c)^2-b^2/(7c-b)^2

Answer 1

Приводим к общему знаменателю:
49с^2/(b-7c)^2-b^2/(b-7c)^2=(7c-b)(7c+b)/(7c-b)^2=(7c+b)/(7c-b)