Question

Найдите сумму x + y,
(2x+3y=8
(X+2y=5

Answer 1

$\displaystyle\mathsf{\left \{ {{2x+3y=8} \atop {x+2y=5}} \right. }$             $\displaystyle\mathsf{\left \{ {{2x+3y=8} \atop {x+2y=5|*(-2)}} \right. }$

$+\displaystyle\mathsf{\left \{ {{2x+3y=8} \atop {-2x-4y=-10}}} \right.$

$\displaystyle\mathsf{-y=-2= > y=2.}\\\displaystyle\mathsf{x+2*2=5= > x=1.}\\\displaystyle\mathsf{Sum: x+y=1+2=3.}$

Answer 2

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$\left \{ {{2x + 3y =8} \atop {x+2y=5}} \right.$     <=>   $\left \{ {{x= \frac{8-3y}{2} } \atop {x = 5-2y}} \right.$    <=>     $\left \{ {{y=2} \atop {x = 5 - 2^. 2 }} \right.$     <=>   $\left \{ {{y=2} \atop {x=1}} \right.$

$\frac{8-3y}{2} = 5-2y\\\\8 - 3y = 10 - 4y\\\\-3y+4y = 10-8\\\\y = 2$

$x+y = 1+2 = 3$

ответ: 3