Q. To verify that the interior angle of a triangle is equal to the sum of the two interior opposite angles.

Hi!

Here is the answer to your query.

In ΔABC

∠A + ∠B + ∠C = 180° [Angle sum property ] .....(1)

Also

∠C + ∠BCD = 180° [Linear Pair ] ....... (2)

Equating (1) and (2)

∠C + ∠BCD = ∠A + ∠B + ∠C

∠BCD = ∠A + ∠B

Hence, exterior angle of a triangle is equal to sum of two interior opposite angles.

Cheers!

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