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If in ΔABC, a = 6, b = 3 and cos(A – B) = 4/5 then its area square units is

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If in  ΔABC, a = 6, b = 3 and cos(A – B) = 4/5 then its area square units is

(a)   8

(b)   9 

(c)   6

(d)  None of these 

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1 Answer

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Best answer

Correct option  (b) 9

Explanation:

Using Napier’s analogy

tan A  - B/2 = a - b/a + b cot C/2 and tan (A - B/2)

cot C/2 = 1

C = 90°

A  = 1/2 absinC = 1/2 .6.3. sin90° = 9 square units

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