Carpentry & Building Construction © 2004

Math Activities :

Self-Check Math Activity 18

Rectangles

Carpenters use their knowledge of rectangles to figure distances and materials needed on a job. A rectangle is a polygon with four right angles and four sides. The opposite sides of a rectangle are equal to each other.

In a rectangle, diagonals drawn between opposite corners are equal in length. The carpenter can use this information to check an area for squareness; that is, to check whether the lines are straight and true.

Terms, Symbols, & Abbreviations
rectangle - a polygon with four right angles and four sides
right angle - an angle of 90 degrees
diagonal - slanted line drawn between opposite corners of a polygon

Practice Exercise

Find the missing angle in the rectangle.

Step 1		A rectangle is a flat figure, or polygon, with four right angles and four sides.
Step 2		Therefore the missing angle is a right angle.
Step 3		A right angle has 90 degrees.

The missing angle is 90 degreees.

Find the missing sides in the rectangle.

Step 1		The opposite sides of a rectangle are equal.
Step 2		Side x is opposite to the side whose length is 4. Therefore x = 4.
Step 3		Side y is opposite to the side whose length is 5. Side y therefore = 5.

Problem Exercises


1.	In Figure A, the length of side y is
		A)	3''.
		B)	5''.
		C)	7''.
		D)	12''.


2.	What is the missing angle in Figure A?
		A)	30º
		B)	45º
		C)	60º
		D)	90º


3.	In Figure A the length of side x is
		A)	12''.
		B)	24''.
		C)	7''.
		D)	14''.


4.	Figure B is not a rectangle because
		A)	it is missing an angle.
		B)	all four sides are not equal.
		C)	the opposite sides are not equal.
		D)	there are no diagonals.


5.	Figure C represents a wall. How can a carpenter figure whether the wall is “square,” meaning that the sides of the wall are straight and meet at right angles?
		A)	Side a equals side b.
		B)	Side b is larger than side a.
		C)	Diagonal c equals diagonal d.
		D)	Diagonal c is larger than side b.