To make the R segment follow a curve in the Z plane, you can use the Follow Me tool in SketchUp. Here's how:

Draw a line from point A to point P to create segment R.
Draw a curve in the Z plane (curve H) that the R segment should follow.
Use the Follow Me tool by selecting the R segment and clicking the Follow Me button in the toolbar.
Click on the H curve so that the R segment follows the curve.
Once the R segment follows the curve, use the Face Intersect tool to create a clear intersection between the R segment and the curve.
Using the Follow Me tool, you can make the R segment follow any path or curve in the Z plane.
Follow Me Tool Examples in SketchUp - The SketchUp Essentials #39

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