Bonsoir,
(4 - 7x)² - (7x + 3)²
= 4² - 2 × 4 × 7x + (7x)² - [(7x)² + 2 × 7x × 3 + 3²]
= 16 - 56x + 49x² - [49x² + 42x + 9]
= 16 - 56x + 49x² - 49x² - 42x - 9
= -98x + 7
(-3z - 1)² - 3z(4z - 5z)
= (-3z)² - 2 × (-3z) × 1 + 1² - 12z² + 15z²
= 9z² + 6z + 1 - 12z² + 15z²
= 12z² + 6z + 1
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Bonsoir,
(4 - 7x)² - (7x + 3)²
= 4² - 2 × 4 × 7x + (7x)² - [(7x)² + 2 × 7x × 3 + 3²]
= 16 - 56x + 49x² - [49x² + 42x + 9]
= 16 - 56x + 49x² - 49x² - 42x - 9
= -98x + 7
(-3z - 1)² - 3z(4z - 5z)
= (-3z)² - 2 × (-3z) × 1 + 1² - 12z² + 15z²
= 9z² + 6z + 1 - 12z² + 15z²
= 12z² + 6z + 1