First slide
Trigonometric equations
Question

If 0x2π and 2cosec2x12y2y+12 then number of ordered pairs of (x,y) is

Moderate
Solution

2cosec2x12y2y+12

2cosec2xy22y+22

2cosec2x(y1)2+12----i

We have

2cosec 2x2 and (y1)2+11

 product 2----ii

From (i) and (ii)

2cosecx2x=2 and (y1)2+1=1 sinx=±1 and y=1 x=π2,3π2 and y=1

Hence, the solution of the given inequality is (x,y)=π2,1,3π2,1

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