Solve this system of equations by graphing: 3x - y = 9 and x + y = 7.

Question

Solve this system of equations by graphing: 3x - y = 9 and x + y = 7. Remember to check yourself. Submit your graph and clearly state the solution to this system. Explain, in detail, as an essay, how you graphed your lines, and what the significance of the intersection point is. 

 

I was wondering if i did this right. Please show me if the way I did it was correct. 

Answer 1

No graphing here. Graph them at desmos.com

Will solve by elimination method instead.

 

Adds the equations together:

 

    3x - y = 9

      x+ y = 7

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

    4x       = 16

 

    x= 4.

 

Per the second equation, when x=4, y = 7 - x = 7 - 4 = 3.

 

Checking, it with the first equation with x=3 and y=4,

3(4) - 3 = 12 - 3 = 9.

 

So the solution to the system is (x=4 , y = 3)

 

Now the first linear equation is 3x - 9 = y when solved for y.

The second linear equation when solved for y is  y = -x + 7.

You can now goto desmos.com and graph those two lines.

They will meet at (4,3)