Question

if two lines intersect prove that vertically opposite angles are equal

Answer 1

In the statement above, it is given that ‘two lines intersect each other’. So, let AB and CD be two lines intersecting at O as shown in Fig. 6.8. They lead to two pairs of vertically opposite angles, namely,

(i) ∠ AOC and ∠ BOD (ii) ∠ AOD and ∠ BOC.



We need to prove that ∠ AOC = ∠ BOD and ∠ AOD = ∠ BOC.

Now, ray OA stands on line CD.

Therefore, ∠ AOC + ∠ AOD = 180° (Linear pair axiom) ………..(1)

Can we write ∠ AOD + ∠ BOD = 180°? (Linear pair axiom)……………(2)

From (1) and (2), we can write

∠ AOC + ∠ AOD = ∠ AOD + ∠ BOD

This implies that ∠ AOC = ∠ BOD

Similarly, it can be proved that ∠AOD = ∠BO

Answer 2

Answer:

Given two lines AB and CD intersect each other at the point O.

To prove: ∠1 = ∠3 and ∠2 = ∠4

Proof:

From the figure, ∠1 + ∠2 = 180°  [Linear pair]  → (1)

∠2 + ∠3 = 180°  [Linear pair]  → (2)

From (1) and (2), we get

∠1 + ∠2 = ∠2 + ∠3

∴ ∠1 = ∠3

Similarly, we can prove ∠2 = ∠4 also.

Step-by-step explanation: