Question

se x+y=10 e x-y=7, dê o valor numérico de : 2x+3y=?

Answer 1

$\left \{ {{x+y=10} \atop {x-y=7}} \right. \\ \\ 2x=17 \\ x= \frac{17}{2} \\ x=8,5$

$\left \{ {{x+y=10 } \right. \\ 8,5+y=10 \\ y=10-8,5 \\ y=1,5$

$S= \left \{ {{X=8,5} \atop {Y=1,5}} \right.$

Logo

$2x+3y \\ 2.8,5 + 3.1,5 \\ 17+4,5 \\ =21,5$