Angle Rules

  1. All the angles of a triangle add up to 180 degrees. So if you have this triangle:

  2. If a line MEETS another line, the two angles it makes with that line add up to 180o.

    These 2 angles are said to be SUPPLEMENTARY

    Supplementary angles add up to 180o.

  3. If a line CROSSES another line, then the angles across from each other are the same.
    Angle ? is 40o because it is across from the 40o angle.

    Angle ? is 150o because it is across from the 150o angle