Question

Пусть (x; у) - решение системы уравнения найдите значение выражения 2x+3y

Answer 1

$\left \{ {{x-3y=3,} \atop {x^{2}-9y^{2} =21.}} \right.$

$\left \{ {{x-3y=3,} \atop {(x-3y)(x+3y) =21.}} \right.$

$\left \{ {{x-3y=3,} \atop {3(x+3y) =21.}} \right.$

$\left \{ {{x-3y=3,} \atop {x+3y =7.}} \right.$

$\left \{ {{2x=10,} \atop {x+3y =7.}} \right.$

$\left \{ {{x=5,} \atop {3y =7-5.}} \right.$

$\left \{ {{x=5,} \atop {3y =2.}} \right.$

$\left \{ {{x=5,} \atop {y = \frac{2}{3} .}} \right.$

$2x+3y=2*5+3* \frac{2}{3} =10+2=12$