Question

What is the solution to this system of equations?

Answer 1

Answer:

  C.  x = 3, y = -6

Step-by-step explanation:

You can divide the second equation by 2. Then you have ...

  x +2y = -9

This gives you a couple of choices for solution. The x-coefficients match, so subtracting one equation from the other eliminates x:

  (x +2y) -(x -2y) = (-9) -(15)

 4y = -24   ⇒   y = -6

Adding the two equations eliminates y:

  (x -2y) +(x +2y) = (15) +(-9)

  2x = 6   ⇒   x = 3

The solution is (x, y) = (3, -6).

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Additional comment

I find it quick and easy to use a graphing calculator to find the solution. Many graphing calculators also make it simple to solve systems of equations in matrix form. Either way, you can obtain a solution in little more than the time it takes to enter the equations (or their coefficients).