Question

How do you find the solution of the system of equations `2x-y= -3` and `x+y=3`?

Answer 1

The solution to this system is : `{(x=0),(y=3):}`

It is easy to see, that the coeficients of y are opposite numbers (-1 and 1) so if you add both sides of the equasions you can get rid of "y".
After adding you get `3x=0`, so `x=0`. Now if you substitute `0` for x in any of the equasion you get `y=3`