Can't figure out how to cut compound angle


An alternative method is to insert a Plane and use an Extruded Cut
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Step 1:
Create a Plane. (Features, Reference Geometry, Plane) select 3 points on the sketch,
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Step 2:
Start a new sketch and draw a large rectangel on the plane.
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Step 3:
Use the rectanle to perform an Extrude Cut (use the Reverse Direction option)
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Step 4:
Repeat these steps to cut the other plane.