SCRA Whole-Testpaper Contributed by Dheeraj updated on Jul 2019

SCRA   Special Class Railway Apprentices    Solved Paper 2009  Mathematics questions with answers,SCRA model question papers,SCRA previous years solved question papers with detailed explanations

 

1.  If √2 cos A = cos B + cos3 B,

√2 sin A = sin B - sin3 B.

Then, |sin (A - B)| is equal to

(a) 1/2

(b) 1/3   (Ans)

(c) 2/3

(d) 1/5

Solution :  sin (A - B) = sin A cos B -  cos A sin B        ............(i)

Substituting the values of cos A and sin A from the given Eq. (i), we have

sin (A - B) = - sin B cos B                                        ............(ii)
                          √2

On squaring and adding given equation, we get

cos2B = 1/3

sin (A - B) = ± 1/3

 

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