Bonsoir,
2/13 = x/39 = 8/x
2/13 = ( 2 × 3 ) / ( 13 × 3 ) = 6/39
2/13 = ( 2 × 4 ) / ( 13 × 4 ) = 8/52
17/23 = x/69 = 34/x
17/23 = ( 17 × 3 ) / ( 23 × 3 ) = 51/69
17/23 = ( 17 × 2 ) / ( 23 × 2 ) = 34/46
15/4 = 60/x = x/52
15/4 = ( 15 × 4 ) / ( 4 × 4 ) = 60/16
15/4 = ( 15 × 13 ) / ( 4 × 13 ) = 195/52
Je te laisse terminer.
Bonne soirée !