Yes
It will be a polygon, although the exact nature of the resulting polygon will depend on the original polygon, its dimensions relative to the triangle, whether or not the two shapes can overlap and so on.
It depends on the relative dimensions of the two object and whether or not they can overlap. I can get anything from a quadrilateral (including a parallelogram) to a 13-sided polygon.
A circle, an ellipse, a triange, any regular polygon with an odd number of sides, a general (ie not a special case) quadrilateral, are some examples
1
never.
width x highest point on the triange then divide by 2 if equilateral/isoceles triange height x width then divide by 2 if right angled triange/scalene triangle
a cone
three
== ==
a triange
a scalene triangle
180 degrees