Réponse :
1 ) a ) [tex]\frac{420}{156} = \frac{35}{13}[/tex]
420 = [tex]2^{2}[/tex] × 3 × 5 × 7 ; 156 = [tex]2^{2}[/tex]× 3 × 13
1 ) b ) [tex]\frac{162}{120} = \frac{27}{20}[/tex]
162 = 2 × [tex]3^{4}[/tex] ; 120 = [tex]2^3}[/tex] × 3 × 5
2 ) a ) [tex]\frac{3}{7}- \frac{1}{21} = \frac{3 (3) + 1 }{21} = \frac{10}{21}[/tex]
2 ) b ) [tex]\frac{1}{-5} - \frac{7}{-3} = \frac{-3 (1) - 5 (7) }{15} = \frac{-3 - 35}{15} = \frac{-38}{15}[/tex]
