1
Select the Create Corner tool 
from the Sketch ribbon group.
2 Click a line, arc, or spline.
3 Mouse over another line to preview the corner that will be created.
If you mouse over a line that is the cross-section edge of a solid or a silhouette edge, it will not change. Only a sketched line will change.
4 Click an intersecting line to trim the lines, or a non-intersecting line to extend the lines.
If the lines intersect, click the part of the intersecting line you want to keep. If the lines do not intersect, you can click anywhere on the line to extend the lines to form a corner.
