How do you solve the system x + y = 2 and 2x + y = -1?

2 Answers
Apr 5, 2018

x=1/3

y=5/3

Explanation:

from this equation

x+y=2

x=2-y

put the value of x in this equation

2x+y=-1

2(2-y)+y=-1

4-4y+y=-1

-3y=-5

y=5/3

x+y=2

x+5/3=2

x=1/3

Apr 5, 2018

x = -2, y = 3

Explanation:

This is a simultaneous equation question. In the interest of time, I will solve it using the elimination method:

x + y = 1

2x + y = -1

To solve using elimination, all we do is literally subtract the bottom line from the top line which gets rid of the y (y-y = 0), giving us:

-x = 2

x = -2

We then substitute (x =-2) into either of the equations:

x + y = 1

(-2) + y = 1

y = 3

And then check that this works, using substituting both values into the second equation.

-2x + y = -1

2(-2) + (3) = -1

-1 =-1, so we know the values are correct!