Fundamental Algebra:
1. Add:
(i) x² – y² – 1 ; y² – 1 – x² ; 1 – x² – y²

The correct answer is: - ( x2 + y2 + 1 )

Answer:

• Step by step explanation:

○        Given:
                         Expression:  x² – y² – 1 ;
y² – 1 – x² ;
1 – x² – y²
○        Step 1:
○        Simplify the expression.
 ( x² – y² – 1 ) + ( y² – 1 – x² ) + (  1 – x² – y² )
 ( x² – y² – 1 ) + ( y² – 1 – x² ) + (  1 – x² – y² )
○        Step 2:
○        Group the like terms.
 ( x² – x² – x² ) + ( y² – y²– y² ) + (  1 – 1 – 1 )
 ( – x² ) + ( – y² ) + ( – 1 )
○        Step 3:
○        Take -1 common from all terms,
            - ( x² + y² + 1 )

•  Final Answer:

          - ( x² + y² + 1 )