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`A = (x + 2)² - (x - 2)²`

`A = (x² + 4x + 4) - (x² - 4x + 4)`$\\$ `A = x² + 4x + 4 - x² + 4x - 4`$\\$ `A = 8x`$\\$

Vậy `A=8x`

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`(2x + 3)² - (2x - 3)²`$\\$ `= [(2x + 3) - (2x - 3)][(2x + 3) + (2x - 3)]`$\\$ `= 6 . 4x`$\\$ `= 24x`$\\$

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`(x + 5)² - (x - 5)² = 80`$\\$ `[(x + 5) - (x - 5)][(x + 5) + (x - 5)] = 80`$\\$ `10 . 2x = 80`$\\$ `20x = 80`$\\$ `x=80:20`$\\$ `x = 4`$\\$

Vậy `x=4`