A system of equations is given below.
2x + 7y = 1
-3x – 4y = 5

Create an equivalent system of equations by replacing the first equation by multiplying the first equation by an integer other than 1, and adding it to the second equation.

Question

A system of equations is given below.
    2x + 7y = 1
    -3x – 4y = 5

        Create an equivalent system of equations by replacing the first equation by multiplying the first equation by an integer other than 1, and adding it to the second equation.

anonymous · Answer

WTF?

anonymous · Answer

What???

anonymous · Answer

Just bored, sorry i don't know the answer i'll go find my friend to help you out he's kinda smarty.

anonymous · Answer

Ok thanks

anonymous · Answer

@undeadknight26 can you help me?

undeadknight26 · Answer

Sorry i know this but its not coming to me right now...

anonymous · Answer

Ok that is ok, do you know anyone that can help me?

undeadknight26 · Answer

@SolomonZelman @hartnn @amistre64

anonymous · Answer

Thanks :)

solomonzelman · Answer

2x + 7y = 1    ---> times 3  ---->   6x    +21y   =  3
 -3x – 4y = 5   ---> times 2  ---->   -6x   -8y    =  10
                                                          -----------------
                                                               0x   +13y  = 13

y=1
can you solve for x?

anonymous · Answer

well if y = 1 then shouldn't x = 0

anonymous · Answer

But all I needed to change was the first equation not both of them

solomonzelman · Answer

why would it be 0, no it's not zero, solve for x by plugging in 1 for y into one of the equations.

anonymous · Answer

Oh sorry I was looking at the very last equation on the bottom right. If y = 1 then x = -3

solomonzelman · Answer

See how I did it?
now do
 2x + 7(1) = 1
-3x – 4(1) = 5

2x+7=1
-3x-4=5

2x=-6    x=-3
-3x=9    x=-3

So y=1  and  x=-3    is right.

solomonzelman · Answer

CLEAR?

anonymous · Answer

Kindof but i only need to change the first equation not both equations

solomonzelman · Answer

You can change both equations if you want to, in your case it's better to change both if you want to do elimination.

anonymous · Answer

But in the next part of the question it tells me to solve it using the new first equation and the origional second equation

solomonzelman · Answer

What?! What a poor school, I think they are referring to the "substitution" like this.

 2x + 7y = 1   ---> x= (-7/2)y+(1/2)
substitute   (-7/2)x+(1/2)   for y.

into -3x – 4y = 5
-3x – 4[(-7/2)x+(1/2)] = 5

and solve for x.

But why would they tell you to substitute it in this type of question?

anonymous · Answer

I am so sorry @SolomonZelman I had to go help wash my dogs, that is why I left. But now I am totally confused

anonymous · Answer

I haven't learned to do all that