on donne r =2/3 ; s = -2/5 et t = -3     Calculer les expressions en détaillant les calculs  r+s+t     r*s*t    rs/t    Donner le résultat sous la forme la plus

Bonjour,

[tex]r+s+t =\dfrac{2}{3}+(-\dfrac{2}{5})+(-3)\\\\r+s+t =\dfrac{2}{3}-\dfrac{2}{5}-3\\\\r+s+t =\dfrac{2\times5}{3\times5}-\dfrac{2\times3}{5\times3}-3\\\\r+s+t =\dfrac{10}{15}-\dfrac{6}{15}-3\\\\r+s+t =\dfrac{10}{15}-\dfrac{6}{15}-\dfrac{45}{15}\\\\r+s+t=-\dfrac{41}{15}[/tex]


[tex]r\times s\times t =\dfrac{2}{3}\times(-\dfrac{2}{5})\times(-3)\\\\r\times s\times t =\dfrac{2}{1}\times(-\dfrac{2}{5})\times(-1)\\\\r\times s\times t =\dfrac{4}{5}[/tex]


[tex]\dfrac{r\times s}{t} =\dfrac{\dfrac{2}{3}\times(-\dfrac{2}{5})}{-3}\\\\\\\dfrac{r\times s}{t} =\dfrac{-\dfrac{4}{15}}{-3}\\\\\\\dfrac{r\times s}{t} =\dfrac{\dfrac{4}{15}}{3}\\\\\\\dfrac{r\times s}{t} =\dfrac{4}{15}\times\dfrac{1}{3}\\\\\\\dfrac{r\times s}{t} =\dfrac{4}{45}[/tex]