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Mathematics

x2 + y2 - 2xy - 1 is equal to :

  1. (x + y - 1) (x - y - 1)

  2. (x + y + 1) (x - y - 1)

  3. (x + y + 1) (x - y + 1)

  4. (x - y + 1) (x - y - 1)

Factorisation

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Answer

x2 - y2 - 2xy - 1

Using the formula

[∵ (x - y)2 = x2- 2xy + y2 ]

= (x2 + y2 - 2xy) - 1

= (x - y)2 - 12

Using the formula

[∵ (x2 + y2) = (x + y)(x - y)]

= ((x - y) + (1))((x - y) - (1))

= (x - y + 1)(x - y - 1)

Hence, option 4 is the correct option.

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