*I didn't understand the video , please explain me*

Hi!

Here is the answer to your question.

**Exterior angle property of a triangle:**

The measure of exterior angle of a triangle is equal to sum of its two interior opposite angles.

Here, ∠ABD is the exterior of ∆ABC and BF||AC.

BF || AC and AB is the transversal,

∠ABE = ∠CAB … (1) (Pair of alternate interior angles)

BF || AC and CD is the transversal,

∠DBE = ∠BCA … (2) (Corresponding angles)

Adding (1) and (2), we get

∠ABE + ∠DBE = ∠BCA + ∠CAB

From the given figure, we have ∠ABE + ∠DBE = ∠ABD

∴ ∠ABD = ∠BCA + ∠CAB

Thus, the measure of exterior angle of a triangle is equal to sum of its two interior opposite angles.

Cheers!

**
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