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rahul

· started a discussion

· 1 Months ago

please provide short solution (Question: 271989.0 )

solution method is very lengthy. i did with same method and it took me more than 2 mins to get the answer.

Question:

If cot A =  12-1   , then the value of sin A cos A is –

Options:
A)

14    

B)

12    

C)

12    

D)

24    

Solution:

Ans: (d)

  

Kriti Sharma

· commented

· 1 Months ago

Cos A = (√2+1)Sin A
Squaring both sides
1- Sin²A = (3+2√2)Sin²A
(4+2√2)Sin²A = 1
Sin²A = (4- 2√2)/8
CosA*SinA = Cot A*Sin²A = (1/(√2-1))*((2-√2)/4) =√2/4
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