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Q.

Find the value of 1 tanA + sinA 1+cosA   from the following choices if cosecA=2  


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a

1

b

2

c

2  

d

1 2   

answer is B.

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Detailed Solution

Given that, cosecA=2  .
Write cosecA=2   in terms of the ratio of sides of the right triangle.
cosecA= 2k 1k = hypotenuse Opposite side  
We know that, cosec A is the ratio of hypotenuse to the opposite side.
With respect to A, form a triangle with opposite side (BC) as 1k and the hypotenuse (AC) as 2k.
Question ImageFind third side AB   by applying Pythagoras theorem.
(base) 2 + (perpendicular) 2 = (hypotenuse) 2  
A C 2 =B C 2 +A B 2 4 k 2 = k 2 +A B 2 A B 2 =4 k 2 k 2 AB= 3 k  
Write sinA,tanA   and cosA   from sides of the triangle for corresponding to angle A.
sinθ= Opposite side Hypotenuse   sinA= BC AC sinA= 1k 2k sinA= 1 2  
We know that, tanθ   is the ratio of opposite side to the adjacent side.
tanA= BC AB tanA= 1k 3 k tanA= 1 3  
And, cosθ= Adjacent side Hypotenuse  .
cosA= AB AC cosA= 3 k 2k cosA= 3 2  
Now, find the value of sinA,tanA and cosA 1 tanA + sinA 1+cosA  .
1 1 3 + 1 2 1+ 3 2   Multiply and take LCM.
3 + 1 2+ 3 3 (2+ 3 )+1 2+ 3 2 3 +3+1 2+ 3 2 3 +4 2+ 3 2(2+ 3 ) 2+ 3 2   Thus, 1 tanA + sinA 1+cosA =2  .
Hence, option 2) is correct.
 
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