How to extrude at an angle in Compass 3D?

Question

3D

Good afternoon!

The goal is to "extrude" a square contour inside the figure, but not parallel to the plane of the contour, but in accordance with the triangular contour on the left side.
Or, in other words, it is necessary to "extrude" a triangular contour inside the figure, starting not from the face, but within the square contour.

Answer 1

try to draw an auxiliary plane, and on it a sketch, and then cut