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Mathematics

The value of (a - b - c)(a - b + c) is:

  1. a2 + b2 + c2 + 2ab

  2. a2 + b2 - c2 - 2ab

  3. a2 + b2 + c2 - 2ab

  4. a2 + b2 - c2 + 2ab

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Answer

(a - b - c)(a - b + c)

= a (a - b + c) - b (a - b + c) - c (a - b + c)

= a(1+1) - ab + ac - ab + b(1+1) - bc -ac + bc - c(1+1)

= a2 + (- ab - ab) + (ac -ac) + b2 + (- bc + bc) - c2

= a2 - 2ab + b2 - c2

Hence, option 2 is the correct option.

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