Angle
Angle is formed by two rays originating from the same point called the vertex of the angle.
Angle Names:
These special angle names are also used to classify triangles.
Acute Angle
Angle with a measure between zero and ninety degrees is called Acute angle.
Right Angle
Angle with a measure of exactly ninety degrees is called a Right angle.
Obtuse Angle
Angle with a measure between ninety and one hundred eighty degrees is called Obtuse angle.
Straight Angle
Angle with a measure of exactly one eighty degrees is called a Straight angle.
Reflex Angle
Angle with a measure between one hundred eighty and three hundred sixty degrees is called Reflex angle.
Angle Relationships:
These special terms give us clues of how given angles relate to each other. Knowing these terms comes in very useful during problem solving.
Adjacent
Two non-overlapping angles that share a side are called adjacent angles.
Complementary
Two angles are complementary if they add up to 90°
Supplementary
Two angles are supplementary if they add up to 180°
Exercise:
In the following picture <XSN is right angle and <KST is straight angle. Given that m(<XSP)=45°, and m(<XST)=140°, calculate measure of angles <KSX, <PSN, and <NST.
Vertical
Vertical-Angles are congruent (have same measure).
