Get the normal vector(angle) on the point

I got the two partial differential function(X direction, Y direction) by using Sobel function in opencv. and then calculated magnitude by using magnitude function.
and get the tangent angle by using phase function.
when I using the phase function I wrote that —> phase(sobel x, sobel y, result, true)

I want calculate normal vector(angle) on the point by using result of phase.
I thought normal = direction / magnitude.
so, I tried … but result looks like wrong.
Can you guys teach to me right method???

makes sense, if direction is a 2d vector,
but dividing angles (phase !) by the resp. vector length – not at all

what do you need the vector for ?

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Thank you for your reply.
I want get the normal degree on the point.

I aleady got the tangent angle. but how get the normal angle of tangent angle(red line)??

and finally I want draw the red line on the image.
blue parabola is edge of canny.

its just theta + 90

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Thank you for your reply. I thought so hardly…

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