SOLUTION: Can you show me how to solve this system of equations: y=3x x+21=-2y by the substitution method?

Question 119807: Can you show me how to solve this system of equations: y=3x
x+21=-2y
by the substitution method?
Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
Start with the given system

Plug in into the first equation. In other words, replace each with . Notice we've eliminated the variables. So we now have a simple equation with one unknown.

Multiply

Subtract 21 from both sides

Add 6x to both sides

Combine like terms on the left side

Divide both sides by 7 to isolate x

Divide

Now that we know that , we can plug this into to find

Substitute for each

Simplify

So our answer is and

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