How can I get Tangential direction Vector in Python?

I can get some info from a Arc.

• FirstPoint 　 [x, y, z]
• LastPoint 　 [x, y, z]
• Center 　　 [x, y, z]
• Axis 　　 　 [x, y, z] # Perpendicular to the plane

How can I get the FirstPoint&LastPoint's tangential direction Vector?

I want to get a intersection Point from two direction vector.

I work in FreeCAD.

Circular arc from A to B with center M and normal vector N.

The tangent directions can be obtained by the cross product.

• Tangent at A: N x (A-M)
• Tangent at B: (B-M) x N

Both correspond to a rotation of 90DEG or -90DEG of the radius vectors around the axis N