Thread: Please check if this is right?

Use substitution to solve:

x=3y-2
2x+4y=16


x-3y=2
(+)2x+4y=16
----------------
3x+1y =18

3x+1y-1y+18-y
3x/3 = 18/3
x=6

6-3y=2
6-3y+3y=2+3y
6/6=6y/6
y=0

Is my answer is right?

Originally Posted by Hayabusa

Use substitution to solve:
x=3y-2
2x+4y=16

try this

eq1 x=3y-2
eq2 2x+4y=16

eq2 - 2(eq1)

..2x+4y=16
-2(x=3y-2)
-----------
0+4y=16-3y+2

or

4y=18-3y

7y=18

y=18/7, now plug in y to either equation to find x

Originally Posted by Hayabusa

Use substitution to solve:

x=3y-2
2x+4y=16
[...]
x=6
[...]
y=0

Is my answer is right?

Well, the answer has to be 'no' as you can see by trying the values you've obtained in the original equations. For example, if x=6 and y=0 then 3y-2=-2 and this isn't equal to x, so the first equation isn't satisfied. 2x+4y=12 and so the second isn't satisfied either, but your answer would have had to be wrong even if only one of the two had failed.

Since you're told to use substitution I think you were being asked to use x=3y-2 in the second equation, so that 2(3y-2)+4y=16 giving 10y-4=16, 10y=20, y=2 and then x=4.

Originally Posted by Math Help

try this

eq1 x=3y-2
eq2 2x+4y=16

eq2 - 2(eq1)

..2x+4y=16
-2(x=3y-2)
-----------
0+4y=16-3y+2

No, 0+4y = 16 - 6y+4