Find the missing length. The triangles in each pair are similar. Please explain.

Idon’t have a clue on how i should understand this i’m in need of assistance.

Which of the following statements is not true about regions? a.) regions have fixed boundaries that are determined by the region's inhabitants.b.) a region can be defined by physical characteristics, such as climate, landform, and vegetation.c.) regions can change over time.d.) a region can be defined by human characteristics, such as language, government, and economic activity.e.) the same location can be considered part of multiple regions.

How do astronomers measure the amount of dark matter in the universe