If the difference d(n) = x(n) ax(n-1), then what is the optimum choice for a = ?

• A. ({ _{xx} (1)}{ _x^2} )
• B. ({ _{xx} (0)}{ _x^2} )
• C. ({ _{xx} (0)}{ _d^2} )
• D. ({ _{xx} (1)}{ _d^2} )