Пусть (x;у) - решение системы уравнения [latex] \left \{ {{x-3y=3,} \atop {x^{2}-9y^{2} =21.}} \right. [/latex] Найдите значение выражения 2x+3y

[latex] \left \{ {{x-3y=3,} \atop {x^{2}-9y^{2} =21.}} \right. [/latex] [latex] \left \{ {{x-3y=3,} \atop {(x-3y)(x+3y) =21.}} \right. [/latex] [latex] \left \{ {{x-3y=3,} \atop {3(x+3y) =21.}} \right. [/latex] [latex] \left \{ {{x-3y=3,} \atop {x+3y =7.}} \right. [/latex] [latex] \left \{ {{2x=10,} \atop {x+3y =7.}} \right. [/latex] [latex] \left \{ {{x=5,} \atop {3y =7-5.}} \right. [/latex] [latex] \left \{ {{x=5,} \atop {3y =2.}} \right. [/latex] [latex] \left \{ {{x=5,} \atop {y = \frac{2}{3} .}} \right. [/latex] [latex]2x+3y=2*5+3* \frac{2}{3} =10+2=12[/latex]