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 :>
