Question

how to construct 180 degree with compass

Answer 1

Thanks for asking the question.
One eighty degree angle can be drawn with the help of a pencil and a ruler. You just have to draw a straight line with the help of ruler and pencil. This is because 180 degree angle is a straight line and you don't need a compass for that.
Hope it helps.

Answer 2

Normally we use a ruler and a pencil to draw 180°, as any point on a straight line includes 180° between the line segments on either side.

However, with a compass we can draw 180° included in a circular sector (semicircle).

Compass is a geometrical figure constructing tool. It has two legs with one having a clamp for holding a sharp pencil.

  Compass is used to draw circular arcs usually and to measure distances.

 To construct a 180 degrees with just a compass, we draw a straight line AB using a ruler and pencil.  We mark a point O on AB.  Then with O as the center draw an arc with a radius of 2 cm (or any other) from the left side of O to right side of O.

    This arc cuts the straight line AB at C and D.  

The angle ∠COD in the sector ACODB is 180°.