Despite the large size of russia and the near abroad, 75% of the people live in 20% of the total area known as the fertile triangle.

The statement is - True.

The majority of the people in Russia live in the are known as the ''Fertile Triangle''. This area is located in the European part of the country, lying between the plains north of the Caucasus Mountains, to St. Petersburg, and to the central part of the Ural Mountains, and connecting these three places gives us a triangular shape of the are.

The ''Fertile Triangle'' is dominated by the Eastern European Plain, or Russian Plain, with the Volga River being the dominant water body in the area. It is a very fertile are, where most of the agriculture in Russia takes place. The biggest cities in the country are located in there, like Moscow, St. Petersburg, and Volgograd, and the biggest population density, by far, in the country is int his area.

the answer would be the third option, "no, ariel should have added 9^2 and 12^2 and compared that to 15^2."

this is found through the pythagorean theorem, which is a^2 + b^2 = c^2.

this is the correct way of solving the problem:

9^2 + 12^2 = 15^2

81 + 144 = 225

225 = 225