2x+3y = 7

Question

4x-3y = -19
6x=12/6
x = -2

this is elimination method. i have few questions, when do we know wen to add or subtract? multiply? how? i don't know nothing.

Answer 1

The idea is to eliminate a variable. YOu add or subtract to do that.

x-y=4
x+y=6 on that add, the y will be elimated.

2x-y=4
5x-y=5
on this, subtract because the signs are the same, they do not add to zero.
it becomes
2x-y=4
-5x+y=-5
then you get -3x=-1..

Now multiplying
2x+3y=7
3x+y=5
if you want to eliminate the y, then multiply the second equation by 3, then subtract. If you want to eliminate the x, then multiply the top equation by 3, and the second equation by 2, then..subtract, and x will go away.