But isn't it supposed to be subtraction when the thing you are removing is positive? in this case 2x
and then addition when it's negative to get rid of it?

-2x is equivalent to + (-2x). Therefore you would need to add 2x to cancel it out to 0.

You could also use the fact that -(-2x) is equivalent to +2x if it makes it more clear to you (or what you were inferring by subtraction)

I cbf reading all the posts, but feel free to PM me with questions if any remain. I will be happy to help.

Ah shoot didn't see it was -2x my bad then it's addition ofc but yeah got same result anyways.

Ok now the real question is, how do I go from k form to general form if it's needed?

I got the other one under control, now I need to know how to go from y=kx+m to Ax+By+C=0

It just tells you to have one side equal to zero. In the form of y = k*x + m (which, really, is the same as By = A*x + C) you just have to throw over y and you're done:
y = k*x + m --> 0 = k*x + m - y --> (rearrange) k*x - y + m = 0

In this case, A is equal to k; B is equal to -1; C is equal to m:

k*x + (-1)*y + m = 0 = a*x + b*y + m

how do you get a=k, b=-1 etc? i need a little more simplified version if you may, english is not my primary language though I do understand it fluently. Just not when it comes to math explanations I guess

In the general form, Ax+By+C=0, A is the coefficient of x, B is the coefficient of y, and C is the constant.
In the k form, y = kx + m, k is the coefficient of x, and m is the constant. y will always have a coefficient of 1 is this form.

Taking the k form, you can move the y term to the other side with kx and m to get general form:



Since y is now negative, it is understood to now have a -1 coefficient, while x still have a coefficient of k, and the constant m.