Area = ab

Area = ½ cd.

Example: d = 5"

c = 6"

Then, ½ × 5" × 6" = 15 sq. in.

n = Number of sides, s = Length of one side, r = Inside radius

Area = ½ nsr

Number of Sides

Area

2

r2

5

1.72047

s = 3.63273

s2 = 3.46408

r2

6

2.59809

s2 = 3.37099

r2

7

3.63395

s2 = 3.31368

r2

8

4.82847

s2 = 3.27574

r2

9

6.18181

s2 = 3.24922

r2

10

7.69416

s2 = 3.22987

r2

11

9.36570

s2 = 3.21539

r2

12

11.19616

Area = ½ [ a (e + d) + bd + ce]

Example: a = 10", b = 3", c = 5", d = 6", e = 8"

Area = ½ [ 10 (8 + 6) + (3 × 6) + (5 × 8)] = 99 sq. in.

The diagonal of a square = A X 1.414

The side of a square inscribed

in a given circle is B X 0.707.

A = 1/2[a(e + d) + bd + ce]

be enclosed in brackets. The reverse is not true. The

values enclosed by parentheses must be calculated

A = 1/2[10(8 + 6) + 3 x 6 + 5 × 8]

before the values within brackets. As an example, find

A = 1/2[10(14) + 18 + 40]

the area of a trapezium using the formula and values

shown in figure 14-37.

A = 1/2[140+18 + 40]

14-20