In a 2D sketch, the Split command splits a selected curve to the nearest intersecting curve, maintaining dimensions. Both segments of the split inherit the Horizontal, Vertical, Parallel, Perpendicular, and Collinear constraints of the original. Equal and Symmetric constraints are broken when necessary.
In a 3D sketch, the Split command splits a line, arc, or spline to an intersection with a face, work plane, or surface.
Splitting near the middle of a curve affects the end point nearest the cursor. When multiple intersections are possible, Inventor selects the nearest one.
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Split

In a 2D sketch, the Trim command trims a curve to the nearest intersecting curves or trims selected geometry as defined by the geometry’s boundaries. Trimming creates a coincident constraint between the end point of the trimmed curve and the boundary curves.
In a 3D sketch, the Trim command trims curves to an intersection with a face, work plane, or surface.
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Trim
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Trim
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Trim

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Trim
Inventor trims all lines and curves that the cursor passes over.

In a 2D sketch, the Extend command extends a curve to the nearest intersecting curve or extends selected geometry as defined by the geometry’s boundaries. Extending creates a coincident constraint between the end point of the trimmed curve and the boundary curves.
In a 3D sketch, the Extend command extends curves to intersect with a face, work plane, or surface.
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Extend
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Extend
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Extend

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Extend
Inventor extends all lines and curves that the cursor passes over.