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Q.

In the given figure, what is the value of 3tanθ2sinα+4cosα  ?


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a

12 5  

b

13 5  

c

12 7  

d

2 5    

answer is A.

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Detailed Solution

Given a figure.
Question ImageIn right triangle RSQ applying Pythagoras theorem to find RS, we get,
R S 2 =S Q 2 +R Q 2 R S 2 = (6) 2 + (8) 2 R S 2 =36+64 R S 2 =100 RS=±10 RS=10   As negative length can be discarded.
Applying Pythagoras theorem in right triangle QPR to find PQ, we get,
P R 2 =P Q 2 +R Q 2 (17) 2 =P Q 2 + (8) 2 P Q 2 =28964 P Q 2 =225 PQ=±15 PQ=15   As negative length can be discarded.
Cosine is a ratio of the side adjacent to the angle α   to the hypotenuse, thus, applying, we get,
cosα= SQ SR cosα= 6 10 cosα= 3 5                          ......(1)   Sine is a ratio of the side opposite to the angle α   to the hypotenuse, thus, applying, we get,
sinα= RQ SR sinα= 8 10 sinα= 4 5                          ......(2)   Tangent is a ratio of the side opposite to the angle θ   to the side adjacent to the angle θ   Thus, applying, we get,
tanθ= RQ PQ tanθ= 8 15                           ......(3)   Putting values from equations (1), (2), (3), we get,
3tanθ2sinα+4cosα=3× 8 15 2× 4 5 +4× 3 5 3tanθ2sinα+4cosα= 8 5 8 5 + 12 5 3tanθ2sinα+4cosα= 12 5  
Thus, the value of 3tanθ2sinα+4cosα   is 12 5  .
Hence, option 1 is correct.
 
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