From the sum of x2 – y2 – 1, y2 – x2 – 1 and 1 – x2 –

1.	From the sum of x2 – y2 – 1, y2 – x2 – 1 and 1 – x2 – y2, subtract -(1 + y2).
Answer» Sum of x² – y² -1, y² – x² – 1 and 1 – x² – y² = x²– y²– 1 + y²– x²– 1 + 1 – x²– y² On combining the like terms, = x²– x²– x²– y² + y²– y²– 1 – 1 + 1 = -x² – y² – 1 Now, subtract -(1 + y²) from -x² – y² -1 = -x² – y² -1 – [-(1 + y²)] = – x²– y²– 1 + 1 + y² = -x² – y² + y² – 1 + 1 = -x²

From the sum of x2 – y2 – 1, y2 – x2 – 1 and 1 – x2 – y2, subtract -(1 + y2).

Answer»

Sum of x² – y² -1, y² – x² – 1 and 1 – x² – y² = x²– y²– 1 + y²– x²– 1 + 1 – x²– y²

On combining the like terms,

= x²– x²– x²– y² + y²– y²– 1 – 1 + 1

= -x² – y² – 1

Now, subtract -(1 + y²) from -x² – y² -1

= -x² – y² -1 – [-(1 + y²)]

= – x²– y²– 1 + 1 + y²

= -x² – y² + y² – 1 + 1

= -x²