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Area of Rectangles and Triangles

As we progress in economics courses, there are some concepts that are best handled geometrically as opposed to (or in addition to) algebraically. We might, for example, need to calculate the area of a triangle, a rectangle, or a trapezoid. Therefore, this document will cover the basics of each, and give examples for practice.

The area of a rectangle or square

A rectangle is a four-sided figure that has two sets of parallel sides, so that we have two sides of one length and two sides of another length; a square is just a special case of a rectangle in which all four sides are the same length. Therefore, the procedure for calculating area is the same no matter whether we are dealing with a rectangle or a square.

The area of a rectangle is calculated as follows:

Area= base × height= b × hArea⁢= base⁢ × height⁢= b⁢ × h

In this formula, the base is the width of the rectangle and the height is simply how tall the rectangle is. For example, if we have a rectangle that is 20 centimeters wide and 10 centimeters tall, its area can be calculated as follows:

Area= 20cm ×10cm= 200cm2Area⁢= 20cm⁢ ×10cm⁢= 200cm2

Note the superscript '2' in our answer; this is because we have multiplied centimeters by centimeters. In economics, we are more likely to be dealing with quantities bought or sold and prices, so don’t worry about it too much for our discussion.

The area of a triangle

A triangle is really just a rectangle cut in half, so our formula is just ½ times the formula for the area of a rectangle:

Area= 12 × b × hArea⁢= 12⁢ × b⁢ × h

For example, the area of a triangle that is 18 units tall and 40 units wide would be calculated as follows:


Area= 12 × 40 × 18= 40 × 182= 360units2Area⁢= 12⁢ × 40⁢ × 18⁢= 40⁢ × 182⁢= 360units2


Use the data in the table below to answer the following questions.

X-variable	Y-variable	Point
0	8	A
0	5	B
30	5	C
0	4	D
40	4	E
0	3	F
30	3	G
0	0	H

Plot the points BFGC on the graph.

Instructions: Click the 4-point shader tool called "BFGC" and then click on the graph. This will place a rectangle on the graph. Click and drag each of the end points of the shaded area until the rectangle highlights the desired region.

Calculate the following area:

The Area BFGC =    units²

Answer 1

3 We will first Plot the graph for points B,F,GC. so that they can be • joined to estimate the area of hectangle. of m in - To 5 10 15 20 25 30 35 40 45 Avea of Rectangle BFGC = Length * Breadth = F G * GC Co. FG= 30-07 > 30 * 2 * cxaxisa? LoG(=5-3 = 60 unit cy-axis) - q , = Area of Rectangle BF GC = 60 unitse NOTE:- Breadth of Rectangle can also be explained as BFE OB-OF = 5-3 = 2 units)