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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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