How do I change -y to y

Apparently times it by -1 will make it y, well simply...

Why?

the reason is negative*negative=positive
other arithmetic rules include
positive*positive=positive
positive*negative=negative

Why not?

Let y be 1.

1*-1 = -1.

Change back the 1.

-1 -> -y

So there!



Edit:

Better proof.

-1 is the inverse of 1. Which means that -1 when added to 1 gives 0.

(1*x) + (-1*x) should therefore give you 0.
(1*x) + (-1*x) = 0
x(1-1) = 0
x * 0 = 0
x = 0
PROVED. 8D

Correct, you multiply it by -1
how do you change 5 to -5?
5 x -1 = -5
or
3.5 x -1 = -3.5
4000003 x -1 = -4000003
etc
Same theory for y
y x -1 = -y

Hope you understand and this helped! :)

Negative times negative is positive.