The mnemonic rule "the bisector is a rat who runs on corners and halves them" describes a concept essence, but does not make recommendations about creation of a bisector. That to draw it, except the rule you need compasses and a ruler.
Instruction
1. Let's say that you need to construct A bisector. Take compasses, put it an edge in a point of A (vertex of angle) and draw a circle of any radius. Where it will cross sides of angle, put the end of B and C.
2. Measure the radius of the first circle. Draw one more, with the same radius, having put compasses in B point.
3. Carry out the following circle (by the size equal previous) with the center in a point of C.
4. All three circles have to be crossed in one point – we will call it F. By means of a ruler carry out the beam passing through points of A and F. It will also be a required bisector of A.
5. There are several rules which will help you with finding of a bisector. For example, it divides the opposite side of a triangle in the relation equal to the relation of two adjacent parties. Two bisectors will be equal in an isosceles triangle, and in any of triangles three bisectors will be crossed in the center of the circle entered in a figure.