Bonjour
1/
(7x+3)^2 -(7x-3)^2
(7x+3+7x-3)(7x+3-7x+3)
(14x)(6)
84x
2)
Soit x = 10
73 = 7x + 3
67 = 7x-3
Donc
73^2 -67^2 =
(7x+3)^2 -(7x-3)^2 = 84x
= 84(10) = 840
3)
Bc^2 = ab^2 + ac^2
(7x+3)^2 = ab^2 + (7x-3)^2
(7x+3)^2 -(7x-3)^2 = ab^2
84x = ab^2
84(21) = ab^2
Ab^2 = 1764
Ab = V1764
Ab = 42