Answer:
1. Two nonadjacent angles formed by two intersecting lines are vertical angles.
2. For all real numbers x,y, and z , if x=y and y=z , then x=z . Two numbers equal to the same number are equal to each other
3. Supplementary angles are two angles whose sum is equal to 180∘.
4. Points which lie on the same line are called collinear points.
5. Adjacent angles are two angles that have a common vertex and a common side but do not overlap. In the figure, ∠1 and ∠2 are adjacent angles. They share the same vertex and the same common side
6. Perpendicular lines form four right angles.
7. The basic geometrical concepts are dependent on three basic concepts. They are the point, line and plane. We cannot precisely define the terms. But, it refers to the mark of the position and has an accurate location.
8. Symmetric Property: if a = b, then b = a. Transitive Property: if a = b and b = c, then a = c.
9. Angle. An angle is formed by two rays with a common endpoint. Each ray is called an arm of the angle. The common endpoint is called the vertex of the angle.
10. The point where two sides of an angle meet is called a vertex.
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