Question

how can angle B cannout be exterior angle
I can't understand it please someone help me​

Answer 1

Answer:

angle b cannot be exterior angle as it lies in the interior of the closed figure

Answer 2

∠ B is Interior angle as it is closed By △ABC. You can see in the figure.

I proved your theorem

Theorem:-

An exterior angle of a triangle is equal to the sum of its interior opposite angles.

Construction:-

Draw ray CE || AB

Given:-

Consider △ ABC, ∠ACD is an

exterior angle, ∠ABC and ∠BAC are

interior angle.

To prove:-

∠ACD = ∠ABC + ∠BAC

Proof:-

since CE || AB

•°• ∠BAC = ∠ACE .......1...{Alternate angle}

•°• ∠ABC = ∠ECD ......2..{ correspondence angle}

but, ∠ACD = ∠ACE + ∠ECD .....3.{Construction}

From 1, 2 and 3

∠ACD = ∠BAC + ∠ABC.

Hence proved that,

∠ACD = ∠A + ∠B