Carpentry & Building Construction © 2004

Angles

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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.

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Two angles are complementary if their sum totals 90 degrees. When two angles total 180 degrees, the angles are supplementary.

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When two straight lines intersect, the angles next to each other total 180 degrees and the angles opposite each other are equal.

 Practice Exercise

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• Angle A is more than 90 degrees and less than 180 degrees. Therefore it is an obtuse angle.
• Angle B is less than 90 degrees. It is an acute angle.
• Angle C is exactly 90 degrees. It is a right angle. Note the symbol where the two lines meet.

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• The two angles in A add up to a straight line, which is 180 degrees. Therefore these angles are supplementary.
• The two angles in B make up a right angle, which is 90 degrees. These angles are complementary.

Problem Exercises

1.		The angles formed when studs are nailed correctly to the top and bottom plates of a wall are
			A)	acute angles.
			B)	right angles.
			C)	obtuse angles.
			D)	supplementary angles.
2.		One example of an obtuse angle is the angle formed
			A)	by two sides of a gable roof.
			B)	by a stud nailed to a sill plate.
			C)	by two walls joined at a corner.
			D)	by a stair stringer and the floor underneath it.
3.		An acute angle may be formed by the
			A)	top of a roof truss.
			B)	coped end of molding.
			C)	riser and tread on a stair.
			D)	intersection of two walls.
4.		Two angles are complementary when their sum equals
			A)	180 degrees.
			B)	120 degrees.
			C)	90 degrees.
			D)	45 degrees.
5.		A 45-degree angle to be cut for a miter joint is a(n)
			A)	acute angle.
			B)	right angle.
			C)	obtuse angle.
			D)	complementary angle.