[tex]\dfrac{21}{10} \times \dfrac{15}{14} = \dfrac{21\times15}{10\times14}\\\\\dfrac{21}{10} \times \dfrac{15}{14} = \dfrac{3 \times \textbf{7} \times 3 \times \textbf{5} }{2 \times \textbf{5} \times 2 \times \textbf{7}}\\\\\dfrac{21}{10} \times \dfrac{15}{14} = \dfrac{3 \times 3 }{2 \times 2}\\\\\dfrac{21}{10} \times \dfrac{15}{14} = \dfrac{9 }{4}[/tex]
Bonne journée !
