Question 190508



Start with the given system of equations:


{{{system(x+y=4,-5x+2y=-6)}}}




Now in order to solve this system by using substitution, we need to solve (or isolate) one variable. I'm going to solve for y.





So let's isolate y in the first equation


{{{x+y=4}}} Start with the first equation



{{{y=4-x}}}  Subtract {{{x}}} from both sides



{{{y=-x+4}}} Rearrange the equation



---------------------


Since {{{y=-x+4}}}, we can now replace each {{{y}}} in the second equation with {{{-x+4}}} to solve for {{{x}}}




{{{-5x+2highlight((-x+4))=-6}}} Plug in {{{y=-x+4}}} into the second equation. In other words, replace each {{{y}}} with {{{-x+4}}}. Notice we've eliminated the {{{y}}} variables. So we now have a simple equation with one unknown.




{{{-5x+(2)(-1)x+(2)(4)=-6}}} Distribute {{{2}}} to {{{-x+4}}}



{{{-5x-2x+8=-6}}} Multiply



{{{-7x+8=-6}}} Combine like terms on the left side



{{{-7x=-6-8}}}Subtract 8 from both sides



{{{-7x=-14}}} Combine like terms on the right side



{{{x=(-14)/(-7)}}} Divide both sides by -7 to isolate x




{{{x=2}}} Divide






-----------------First Answer------------------------------



So the first part of our answer is: {{{x=2}}}










Since we know that {{{x=2}}} we can plug it into the equation {{{y=-x+4}}} (remember we previously solved for {{{y}}} in the first equation).




{{{y=-x+4}}} Start with the equation where {{{y}}} was previously isolated.



{{{y=-(2)+4}}} Plug in {{{x=2}}}



{{{y=-2+4}}} Multiply



{{{y=2}}} Combine like terms 




-----------------Second Answer------------------------------



So the second part of our answer is: {{{y=2}}}










-----------------Summary------------------------------


So our answers are:


{{{x=2}}} and {{{y=2}}}


which form the point *[Tex \LARGE \left(2,2\right)] 









Now let's graph the two equations (if you need help with graphing, check out this <a href=http://www.algebra.com/algebra/homework/Linear-equations/graphing-linear-equations.solver>solver</a>)



From the graph, we can see that the two equations intersect at *[Tex \LARGE \left(2,2\right)]. This visually verifies our answer.





{{{
drawing(500, 500, -10,10,-10,10,
  graph(500, 500, -10,10,-10,10, (4-1*x)/(1), (-6--5*x)/(2) ),
  blue(circle(2,2,0.1)),
  blue(circle(2,2,0.12)),
  blue(circle(2,2,0.15))
)
}}} graph of {{{x+y=4}}} (red) and {{{-5x+2y=-6}}} (green)  and the intersection of the lines (blue circle).