SOLUTION: 2x+y=9 -3x+2y=4

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: 2x+y=9 -3x+2y=4      Log On


   



Question 120624: 2x+y=9
-3x+2y=4

Answer by nabla(475) About Me  (Show Source):
You can put this solution on YOUR website!
Solve the first equation for y:
y=-2x%2B9
Substitute this y into the second equation:
-3x%2B2%28-2x%2B9%29=4
-7x=-14 Combine terms on the left, subtract 19 from both sides
x=2 Divide both sides by -7.
Now, substitute this value of x into the first equation where we solved for y in terms of x: y=-2%282%29%2B9=-4%2B9=5.
This gives the solution set S:{2,5}.

Additionally, we could solve this system through techniques of linear algebra as follows:
Matrix:
|2 1 9|
|-3 2 4|
(3/2)R1+R2->
|2 1 9|
|0 7/2 35/2|
(1/2)R1->
|1 1/2 9/2|
|0 7/2 35/2|
(2/7)R2->
|1 1/2 9/2|
|0 1 5 |
-1/2R2+R1->
|1 0 2 |
|0 1 5 |
Making S={2,5} the only solution.