bjr
99² = (100 - 1)² = 100² - 2*100*1 + 1² = 10 000 - 200 + 1 = 9801
puisque (a-b)² = a² - 2ab + b²
idem
999² = (1000 - 1)² = 1000² - 2*1000*1 + 1² = ...
et
1001² = (1000 + 1)² = 1000 + 2*1000*1 +1² = ...
puisque (a+b)² = a² + 2ab + b²
95 x 105 = (100 - 5) (100 +5) = 100² - 5² = ...
car (a-b) (a+b) = a² - b²