| a b |
+ | c d |
= | a × | 1 b |
+ | c × | 1 d |
= | ??? on ne peut additionner directement des fractions |
| a b |
+ | c d |
= | a × d b × d |
+ | c × b d × b |
= | ?? on commence par égaliser les dénominateurs |
| a b |
+ | c d |
= |
| + |
| = | ? on factorise les dénominateurs égaux : | 1 b × d |
| a b |
+ | c d |
= |
| = | a × d + c × b b × d |
| a b |
× | c d |
= | a × | 1 b |
× c × | 1 d |
= | a × c × | 1 b × d |
= | a × c b × d |