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Questions  

If 0<x,y<π and cosx+cosycos(x+y)=32 then  sinx+cosy is equal to

a
12
b
1+32
c
32
d
1-32

detailed solution

Correct option is B

2cos⁡x+y2cos⁡x−y2−2cos2⁡x+y2−1=32⇒ 2cos⁡x+y2cos⁡x−y2−2cos2⁡x+y2=12⇒4cos⁡x+y2cos⁡x−y2−4cos2⁡x+y2=1=cos2⁡x−y2+sin2⁡x−y2⇒4cos2⁡x+y2+cos2⁡x−y2−4cos⁡x+y2cos⁡x−y2+sin2⁡x−y2=0⇒cos⁡x−y2−2cos⁡x+y22+sin2⁡x−y2=0⇒ sin⁡x−y2=0⇒x=y⇒ cos⁡x−y2=2cos⁡x+y2  Now. put x=y ⇒ cos⁡x=12=cos⁡y∴ sin⁡x+cos⁡y=32+12=3+12

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