Question

How can you reflect over X=Y

Answer 1

x = y is the same thing as y = x.

When reflecting over y = x, the formula is (x,y) --> (y,x). Basically, the x-coordinate and y-coordinate change places. 

For example, (-2, 0) would become (0, -2).

Hope this helps!

Answer 2

If you want to reflect a function over y = x line, write x in terms of y first and then interchange y with x.
For example,
If you want to reflect y = 2x+3, write it as,
y = 2x + 3
y-3 = 2x
∴ x = (y-3)/2 
Now, interchange x and y
∴ y = (x-3)/2 

Therefore, y = (x-3)/2  is the reflection of y = 2x+3 over X = Y line.