Question

Solve the system using elimination.
X + 7y = 25
2x - 7y = -13

Answer 1

`(4;3)`

Explanation:

Add the two equations together

`I+II: x+7y+2x-7y=25-13 \rightarrow 3x=12\rightarrow x =4`

At this point i'd rather replace x=4 in the first equation to get
`4+7y=25 \rightarrow 7y=21 \rightarrow y=3`

To keep eliminating you multiply the first by 2 and subtract the second

`2* I -II: 2x+14y-2x-(-7y)=50-(-13)\rightarrow 21y=63 \rightarrow y=3`