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m∠A + m∠B = m∠B + m∠C  

Example: Δ ABC is isosceles at B

⇒ m∠A = m∠C

⇔ m∠A + m∠B = m∠B + m∠C  

So:  m∠A + m∠B = m∠B + m∠C ⇒ m∠A = m∠C

P/s: sorry, my writing skill is not very good, but u can use the above ideas to write

Ok done. Thank to me :>

the answer is vanilla

step-by-step explanation: