Hi! how do u know to add or subtract in an equation. for example. x+2y=8. and u want x to go to the right side. so what should i use add x on the other side or subtract x. plz me. & regards, kevin

You can always add or subtract same value to/from both sides of equation. The same is true about multiplication and division.

In your case you have to subtract x from both sides of equation in order to get rid of it on the left side:



But it's easier to remember that if you want to move some member of equation to other side, you just have to change it's sign. Let's practice a bit using your equation (I have added "plus" signs where they are usually omitted to better understend what's going on):


Move 2y to the right side:


Move 8 to the left side:


Move both x and 2y to the right side:

These graph is cross the yaxis and x axis two ways.