How to find intersection between one line and its perpendicular passing by another point

Hi,

I cannot find a simple solution to find the coordinates of point d

I know the coordinates of a, b and c .

I need to know where the blue line passing by point c will cross the red line with angle 90 degrees (find d point)

Could someone help me ??

Answer 1

[Joseph Cheng]

you can follow the computation found here: https://diego.assencio.com/?index=ec3d5dfdfc0b6a0d147a656f0af332bd