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EXAMPLE 6

Find the area of an equilateral triangle having perimeter 78.

Solution

i) The perimeter of an equilateral triangle = 78 units
\ Its side measures 26 units

Using the formula ,

\ D = 1/2 (26)2 sin 600 = 292.7 sq. units.

ii) Let s = semi perimeter, then s = 1/2 (78) = 39 units


iii) The non trigonometric solution is

EXAMPLE 7

In D ABC, a = 18 cms, b = 24 cms and c = 30 cms. Find sin A.

Solution

In this case 2S = 18 + 24 + 30 = 72 cms. \ s = 36 cms

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Index

3. 1 Solving Right Triangles
3. 2 Law of Cosines
3. 3 Law of Sines
3. 4 The Ambiguous Case of Law of Sines

3. 5 Areas of Triangles
Supplementary Problems

Chapter 4





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