Identify the postulate illustrated by the statement: Line ST connects point S and point T

Which system of linear inequalities is represented by the graph? !

International calls require the use of a country code. many country codes a 3-digit numbers. country codes do not begin with a 0 or 1. there are no restrictions on the second and third digits. how many different 3-digit country codes are possible?

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).