Question

If you were to use the substitution method to solve the following system, choose the new equation after the expression equivalent to x from the second equation is substituted into the first equation. 3x + 2y = −21 x − 3y = 4

Answer 1

Hello,

$\left \{ {{3x+2y=-21} \atop {x-3y=4}} \right. \\\\ \left \{ {{3x+2y=-21} \atop {x=4+3y}} \right. \\\\ \left \{ {{3(4+3y)+2y=-21} \atop {x=4+3y}} \right. \\\\ \left \{ {{12+9y+2y=-21} \atop {x=4+3y}} \right. \\\\ \left \{ {{12+11y=-21} \atop {x=4+3y}} \right. \\\\ \left \{ {{11y=-21-12} \atop {x=4+3y}} \right. \\\\ \left \{ {{11y=-33} \atop {x=4+3y}} \right. \\\\ \left \{ {{y=-3} \atop {x=4+3(-3)}} \right. \\\\ \left \{ {{y=-3} \atop {x=5}} \right. \\\\ Sol=\{(5,-3)\}$