If sin x = , cos y = , where x and y both lie in second quadrant, find the value of sin(x + y)?

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AAI ATC Junior Executive 25 March 2021 Official Paper (Shift 3)
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Answer (Detailed Solution Below)

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Detailed Solution

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Given:

sin x =  and cos y = 

Formula Used:

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

sin2x + cos2x = 1

Calculation:

We know that,

sin2x + cos2x = 1

⇒ 

⇒ 

⇒ cos2x = 

⇒ cos2x = 

⇒ cos x = 

⇒ cos x = 

Since x in IInd  quadrant. 

So, cos x is negative.

⇒ cos x = 

⇒ sin2y + cos2y = 1

⇒ sin2y = 1 - cos2y

⇒ sin2y = 

⇒ sin2y = 

⇒ sin2y = 

⇒ sin y = 

⇒ sin y = 

Since y lies in IInd quadrant,

So, sin y is positive.

⇒ sin y = 

Now, Putting the values of sin x, cos x, sin y, cos y

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

⇒ sin (x + y) = 

⇒ sin (x + y) = 

⇒ sin (x + y) = 

⇒ sin (x + y) = 

∴ The value of sin(x + y) is 

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