Question

If two straight lines intersect each other, prove that the ray opposite to the bisector of one of the angles thus formed bisects the vertically opposite angle.

Answer 1

Let AB and CD intersect at a point O

Also, let us draw the bisector OP of .

Therefore,

Also, let’s extend OP to Q.

We need to show that, OQ bisects.

Let us assume that OQ bisects, now we shall prove that POQ is a line.

We know that,

and are vertically opposite angles. Therefore, these must be equal, that is:

and are vertically opposite angles. Therefore,

Similarly,

We know that:

Thus, POQ is a straight line.

Hence our assumption is correct. That is,

We can say that if the two straight lines intersect each other, then the ray opposite to the bisector of one of the angles thus formed bisects the vertically opposite angles.