i can't understand the the video.

plzz explain

The video represents the proof of the angle sum property of a triangle.

I have explained it again. Just go through it.

Consider the ∆PQR, let ∠1, ∠2, ∠3 be its interior angles.

To prove angle sum property of any triangle it is required to prove ∠1 + ∠2 + ∠3 = 180°.

For this extend QP to same point. Also draw a ray through P that is parallel to QR.

Now, PX||QR

∴ ∠5 = ∠3 (alternate interior angle) ... (1)

∠6 = ∠2 (corresponding angles) ... (2)

SPQ is a line segment. PX ray and PR segments stand at point P on it.

∠6 + ∠5 + ∠1= 180° [Linear pair]

⇒ ∠2 + ∠3 + ∠1 = 180° [Using (1), (2)]

⇒ ∠1 + ∠2 + ∠3 = 180°

This shows that the sum of interior angles ∆PQR is 180°.

This is true for any triangle. This is called angle sum property of a triangle.

Hope! This will help you to understand the concept. If you face some problem, write the specific step (s) so that we can provide you meaningful help.