Ответ:

4 * ( X + 1 ) - 4 * ( X - 1 ) = X^2 - 1

4X + 4 - 4X + 4 = X^2 - 1

8 = X^2 - 1

X^2 - 9 = 0

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(X - 3)*( X + 3) = 0

X - 3 = 0 ---> X = 3

X + 3 = 0 ---> X = ( - 3 )

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Ответ 3 и ( - 3 )