This chapter covers the calculation of the perimeter and area of selected plane figures.

EO 1.3

STATE the definition of the following types of triangles:

a. Equilateral

b. Isosceles

c. Acute

d. Obtuse

e. Scalene

EO 1.4

Given the formula, CALCULATE the area and the perimeter of each of the following basic geometric shapes:

a. Triangle

b. Parallelogram

c. Circle

The terms and properties of lines, angles, and circles may be applied in the layout, design, development, and construction of closed flat shapes. A new term, plane, must be understood in order to accurately visualize a closed, flat shape. A plane refers to a flat surface on which lies a straight line connecting any two points.

A plane figure is one which can be drawn on a plane surface. There are many types of plane figures encountered in practical problems. Fundamental to most design and construction are three flat shapes: the triangle, the rectangle, and the circle.

Triangles

A triangle is a figure formed by using straight line segments to connect three points that are not in a straight line.The straight line segments are called sides of the triangle.

Examples of a number of types of triangles are shown in Figure 8. An equilateral triangle is one in which all three sides and all three angles are equal. Triangle ABC in Figure 8 is an example of an equilateral triangle. An isosceles triangle has two equal sides and two equal angles (triangle DEF). A right triangle has one of its angles equal to 90 and is the most important triangle for our studies (triangle GHI). An acute triangle has each of its angles less than 90 (triangle JKL). Triangle MNP is called a scalene triangle because each side is a different length. Triangle QRS is considered an obtuse triangle since it has one angle greater than 90. A triangle may have more than one of these attributes. The sum of the interior angles in a triangle is always 180.

Figure 8 Types of Triangles