Question

How do you solve the system of equations `-2x+4y=7` and ##?

Answer 1

Suppose the second equation was : `4x-y=0`
then
`color(white)("XXX")(x,y)=(1/2,2)`

Explanation:

The only way to clear this question (after a year with no correction) seems to be to add the missing component. The additional equation `4x-y=0` was completely arbitrary.

[1]`color(white)("XXX")-2x+4y=7`
[2]`color(white)("XXX")4x-y=0`

Multiplying [1] by `2`
[3]`color(white)("XXX")-4x+8y=14`

Adding [2] and [3]
[4]`color(white)("XXX")7y=14`

Dividing both sides of [4] by `7`
[5]`color(white)("XXX")y=2`

Substituting `2` for `y` in [2]
[6]`color(white)("XXX")4x-2=0`

[7]`color(white)("XXX")4x=2`

[8]`color(white)("XXX")x=1/2`