SOLUTION: {3x+4y=9 y=x-3 it says to solve the system by using substitution idk how to do that... please help

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Question 198719This question is from textbook The shapes of algebra
: {3x+4y=9
y=x-3

it says to solve the system by using substitution
idk how to do that... please help This question is from textbook The shapes of algebra

Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
3x%2B4y=9 Start with the first equation.


3x%2B4%28x-3%29=9 Plug in y=x-3 into the first equation. In other words, replace each y with x-3. Notice we've eliminated the y variables. So we now have a simple equation with one unknown.


3x%2B4x-12=9 Distribute


7x-12=9 Combine like terms on the left side


7x=9%2B12Add 12 to both sides


7x=21 Combine like terms on the right side


x=%2821%29%2F%287%29 Divide both sides by 7 to isolate x


x=3 Divide


Now that we know that x=3, we can plug this into y=x-3 to find y


y=x-3 Start with the second equation.


y=%283%29-3 Plug in x=3


y=0 Subtract


So our solutions are x=3 and y=0 which form the ordered pair



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+-5%2C+5%2C+-5%2C+5%2C+%289-3x%29%2F4%2C+x-3%29+ Graph of 3x%2B4y=9 (red) and y=x-3 (green)