If 0 < θ , ϕ < π 2 , x = ∑ n = 0 ∞ cos 2 n θ , y = ∑ n = 0…

If 0<θ,ϕ<π2,x=n=0cos2nθ,y=n=0sin2nϕ and z=n=0cos2nθ·sin2nϕ then :
  1. xy-z=x+yz
  2. xy+yz+zx=z
  3. xy+z=x+y z
  4. xyz=4

Solution

x=11-cos2θsin2θ=1x

Also, cos2θ=1y & 1-sin2θcos2θ=1z

So, 1-1x×1y=1zzxy-1=xy ......i

Also, 1x+1y=1  x+y=xy ......ii

From i and ii

xy+z=xyz=x+yz

Asked in: JEE Main 2021 (25 Feb Shift 1)

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