confusing myself with intersecting lines

[yet2spark]

[solved] confusing myself with intersecting lines

I know this is basic, but I can't get my head around it.

If you have two straight lines

x+y=12
and
x-y=4

they intersect when x=8 and y=4

so x+y = x-y at (8,4)

Seems obvious. Where I'm confused is if I plug these values into the equation

8+4 = 8-4 which is never

Can someone help me understand this?

 

[yet2spark]

[solved]

Duh!

It's one of those questions, as soon as you give voice to it, the answer is obvious.

it's not x+y = x-y

it's (x+y)/12 = (x-y)/4

Sorry to waste your time

 

[yet2spark]

lol, just done that