Question 118576
Start with the given system

{{{3x+2y=20}}}
{{{x=-4y}}}




{{{3(-4y)+2y=20}}}  Plug in {{{x=-4y}}} into the first equation. In other words, replace each {{{x}}} with {{{-4y}}}. Notice we've eliminated the {{{x}}} variables. So we now have a simple equation with one unknown.



{{{-12y+2y=20}}} Multiply



{{{-10y=20}}} Combine like terms on the left side



{{{y=(20)/(-10)}}} Divide both sides by -10 to isolate y




{{{y=-2}}} Divide





Now that we know that {{{y=-2}}}, we can plug this into {{{x=-4y}}} to find {{{x}}}




{{{x=-4(-2)}}} Substitute {{{-2}}} for each {{{y}}}



{{{x=8}}} Simplify



So our answer is {{{x=8}}} and {{{y=-2}}}