The biggest problem for the rulers of the ottoman empire beginning in the late-1700s was

Religious and ethnical problems.

It was one of the largest empires of the world with many different ethnicities. The problem was to unite people under one rule.

Another problem was communication. It was hard to transfer knowledge and news to all parts of the empire because it was too large.

Ethnic and religious rivalry :).

reflecting point a across the origin negates both of its coordinates.

b = (5, -4)