How do you Solve and Check

-y=2x and 3x+y=20

from
-y=2x
y=-2x
then you'll substitute to this
3x+(-2x)=20
x=20

y=-2(20)
=-40

to check you'll just substitute the answers you got to the original eq then if the result is eq then you got it right

-(-40)=2(20)
40=40

3(20)+(-40)=20
60-40=20
20=20

you could also check by graphing it and the point of intersection should be the points (20,-40) but sometimes graphing is not accurate if the measurement of units are not equal

-y=2x
y=-2x (divide by -1)
substitute that in the other equation
3x+(-2x)=20
3x-2x=20
x=20
substitute that in the first equation
-y=2(20)
-y=40
y=-40
x=20, y=-40
substitute them both into the first equation
-(-40)=2(20)
40=40

How do you Solve and Check ?

- y = 2x
and
3x + y = 20

solve for y in the first equation...

y = - 2x

substitute...

3x - 2x = 20

x = 20

y = - 40

substitute these values in both equation to check...make a contribution

(20, - 40)

qed

-y=2x
-y-2x=0
y+3x=20
x=20
y=-2x
y=-40
Cheking
-(-40)=2(20)
40=40 OK
-40+3(20)=20
-40+60=20
20=20 OK