Question

Use either substitution or elimination to solve
3x-7y=5
x+3y=-1
I used elimination..and got it wrong..I don't see how you can use two different ways of solving and get the same answer...Please explain..Thanks!

Answer 1

x+3y=-1

x=-1-3y

--------------------


3x-7y=5


3(-1-3y)-7y=5


-3-9y-7y=5


-16y-3=5


-16y=5+3


-16y=8


y=8/(-16)


y=-1/2

----------------------


x=-1-3y


x=-1-3(-1/2)


x=-1+3/2


x=-2/2+3/2


x=(-2+3)/2


x=1/2


So the solutions are x=1/2 and y=-1/2

Answer 2

Thanks! but that's substitution, what about elimination?

Answer 3

3x-7y=5
x+3y=-1



3x-7y=5
-3(x+3y)=-3(-1)



3x-7y=5
-3x-9y=3


-16y=8
y=8/(-16)
y=-1/2

------------------

x+3y=-1


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


x-3/2=-1


x=-1+3/2


x=1/2

Answer 4

Thanks I understand it so much better now!!(:

Answer 5

yw