what is perpendicular to y=1x

Nice answer, flflvm97

However....y = x is it's own inverse......since the inverse function reverses the original coordinates, all the points  on the "inverse" lie on the original function, itself.....

y=x

The gradient for equation perpendicular to another is always $$-\frac{1}{m}$$

m being the gradient of original function.

gradient of y=x is 1

Therefore, $$-\frac{1}{1}$$=-1

So it's y=-x which is inverse to the original function.