Question

Does the system have one solution, no solution, or infinitely many? Use your substitution to justify your answer

x+2y= -10
-x+2y= -2

Answer 1

Answer: It has one solution. The solution is (x,y) = (-4,-3)

Add up the equations doing so straight down

x + -x = 0x = 0 so the x terms go away

2y + 2y = 4y

-10 + (-2) = -12

We end up with 4y = -12 so y = -3 after you divide both sides by 4. Use this y value to find the value of x

x+2y = -10

x + 2(-3) = -10

x - 6 = -10

x = -10+6

x = -4

The single solution is (x,y) = (-4,-3)

As a check, plug this solution into each equation to see if you get a true statement or not. Let's do so with the first equation

x+2y = -10

-4 + 2(-3) = -10

-4 - 6 = -10

-10 = -10 .... true

and then the second equation

-x+2y = -2

-(-4) + 2(-3) = -2

4 - 6 = -2

-2 = -2 .... true

both equations are true, so the solution is confirmed