SOLUTION: please help me solve this problem use the substitution method to solve the linear system here is the promblem Y=x-4 3x-y=-8 what do you do frist

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Question 120666: please help me solve this problem


use the substitution method to solve the linear system
here is the promblem

Y=x-4
3x-y=-8
what do you do frist
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
Start with the given system
3x-y=-8
y=x-4



3x-%28x-4%29=-8 Plug in y=x-4 into the first 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.


3x-x%2B4=-8 Distribute the negative


2x%2B4=-8 Combine like terms on the left side


2x=-8-4Subtract 4 from both sides


2x=-12 Combine like terms on the right side


x=%28-12%29%2F%282%29 Divide both sides by 2 to isolate x



x=-6 Divide




Now that we know that x=-6, we can plug this into y=x-4 to find y



y=%28-6%29-4 Substitute -6 for each x


y=-10 Simplify


So our answer is x=-6 and y=-10 which also looks like



Notice if we graph the two equations, we can see that their intersection is at . So this verifies our answer.


+graph%28+500%2C+500%2C+-10%2C+10%2C+-12%2C+10%2C+%28-8-3x%29%2F-1%2C+x-4%29+ Graph of 3x-y=-8 (red) and y=x-4 (green)