Maths-
General
Easy

Question

If the matrix open square brackets table row 0 cell 2 beta end cell gamma row alpha beta cell negative gamma end cell row alpha cell negative beta end cell gamma end table close square brackets is orthogonal, then -

  1. alpha = ±fraction numerator 1 over denominator square root of 2 end fraction    
  2. beta = ±fraction numerator 1 over denominator square root of 6 end fraction    
  3. gamma = ± fraction numerator 1 over denominator square root of 3 end fraction    
  4. all of these    

The correct answer is: all of these


    Let A = open square brackets table row 0 cell 2 beta end cell gamma row alpha beta cell negative gamma end cell row alpha cell negative beta end cell gamma end table close square brackets, A' = open square brackets table row 0 alpha alpha row cell 2 beta end cell beta cell negative beta end cell row gamma cell negative gamma end cell gamma end table close square brackets
    Since A is orthogonal, therefore AA' = I
    rightwards double arrow open square brackets table row 0 cell 2 beta end cell gamma row alpha beta cell negative gamma end cell row alpha cell negative beta end cell gamma end table close square brackets open square brackets table row 0 alpha alpha row cell 2 beta end cell beta cell negative beta end cell row gamma cell negative gamma end cell gamma end table close square brackets=open square brackets table row 1 0 0 row 0 1 0 row 0 0 1 end table close square brackets
    rightwards double arrow open square brackets table row cell 4 beta squared plus gamma squared end cell cell 2 beta squared minus gamma squared end cell cell negative 2 beta squared plus gamma squared end cell row cell 2 beta squared minus gamma squared end cell cell alpha squared plus beta squared plus gamma squared end cell cell alpha squared minus beta squared minus gamma squared end cell row cell negative 2 beta squared plus gamma squared end cell cell alpha squared minus beta squared minus gamma squared end cell cell alpha squared plus beta squared plus gamma squared end cell end table close square brackets
    = open square brackets table row 1 0 0 row 0 1 0 row 0 0 1 end table close square brackets
    Equation the corresponding elements, we have
    open table row cell 4 beta to the power of 2 end exponent plus gamma to the power of 2 end exponent equals 1 end cell row cell 2 beta to the power of 2 end exponent minus gamma to the power of 2 end exponent equals 0 end cell end table close curly bracketsrightwards double arrow beta equals plus-or-minus fraction numerator 1 over denominator square root of 6 end fraction comma gamma equals plus-or-minus fraction numerator 1 over denominator square root of 3 end fraction
    alpha to the power of 2 end exponent plus beta to the power of 2 end exponent plus gamma to the power of 2 end exponent equals 1 rightwards double arrow alpha to the power of 2 end exponent plus fraction numerator 1 over denominator 6 end fraction plus fraction numerator 1 over denominator 3 end fraction equals 1 rightwards double arrow a equals plus-or-minus fraction numerator 1 over denominator square root of 2 end fraction
    Hence (D) is correct answer.

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