RRB NTPC Mains or Stage 2 Model Paper 10 with solutions

Question : 36 of 120

Marks: +1, -0

If A = cos x cos y, B = sin x sin y and C =

sin^2 x

sin2 y, what is the value of

A^2 – B^2?

Solution:

(b)

A^2 – B^2 = cos^2 x . cos^2 y – sin^2 x . sin^2 y

= (cos x . cos y + sin x . sin y)

(cos x . cos y – sin x . sin y)

= cos (x – y) . cos (x + y)

= cos^2 x – sin^2 y = 1 – sin^2 x – sin^2 y

= 1 – (sin^2 x + sin^2 y) = 1 – C

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