Bonjour,
(7x + 4) * (4x - 7)
= 28x² - 49x + 16x - 28
= 28x² - 33x - 28
(x - 6) * (x + 6)
= x² - 36
(9x - 4)²
= 81x² - 72x + 16
(10x + 6)²
= 100x² + 120x + 36
- (6x - 6)²
= - (36x² - 72x + 36)
= - 36x² + 72x - 36
(1/9x + 6/7) * (1/9x - 6/7)
= 1/81x² - 36/49
