If two lines intersect, prove that the vertically opposite angles are equal.
Solution.
It is given that if two lines intersect, the vertically opposite angles are equal.
Proof:
Now let AB and CD be two lines intersecting at point O.
From the figure, we have two pairs of vertically opposite angles namely:
(i) and
(ii) and
Now we have to prove that
And
Now ray OA stands on line CD
… (i) (linear pair angles)
Similarly, can we write
… (ii) (linear pair angles)
From equation (i) and (ii) comparing
Similarly, we can prove that
Hence Proved.