The first book to describe various types of government and citizenship

The politics.

Explanation:

Aristotle´s The Politics is the first and most important systematic treaty on the various forms of government —an analysis of each kind of government known at the time, their virtues and vices and the desirability of each— and on what constitutes a citizen and what rights should be given to a citizen.

herodotus taught this. herodotus was an ancient greek historian who was born in halicarnassus in the persian empire. he is known for having written the book the histories, a detailed record of his "inquiry" on the origins of the greco-persian wars.

the perimeter of a triangle is 69 cm. side a is 5 cm shorter than side b. side c is twice as long as side a. find the length of each side. i need to know how to do it in 2 equations.  

equations:

a = b-5

c = 2a

a + b + c = 69