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Let x,y,z belong [-1,1] be such that sin^-1 x+sin^-1 y+sin^-1 z=3pi/2 Find the value of , x^2018+y^2019+z^2020

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Solution:     For any  xin[-1,1] , the maximum value of sin^-1x is pi /2

               and it attains this value at x=1

            	herefore       sin^-1xleq pi /2   ,  sin^-1yleq pi /2  , sin^-1zleq pi /2  forall  x,y,zin[-1,1]

              Rightarrow        sin^-1x+sin^-1y+sin^-1zleq 3pi /2    forall   x,y,zin[-1,1]

             Rightarrow     sin^-1x+sin^-1y+sin^-1z=3pi /2

            Rightarrow     sin^-1x=pi /2    ,     sin^-1y=pi /2  , sin^-1z=pi /2

            Rightarrow    x=y=z=1

          Rightarrow       x^2018+y^2019+z^2020=1^2018+1^2019+1^2020=3

 

 

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Deependra Verma

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