Carpenters use angles in measurement, layout, and installations. An angle is formed by two lines that meet at a given point. Two walls that meet at a corner create an angle. So do two sides of a gable roof. Angles are measured in degrees. An acute angle is an angle that is less than 90 degrees. A right angle measures exactly 90 degrees. A symbol that looks like a square may be drawn on the angle to indicate that it is a right angle. An obtuse angle measures more than 90 degrees but less than 180 degrees.
Two angles are complementary if their sum totals 90 degrees. When two angles total 180 degrees, the angles are supplementary.
When two straight lines intersect, the angles next to each other total 180 degrees and the angles opposite each other are equal.