In the given figure, side BC of ΔABC is produced to D.If ∠ACD=128∘ and ∠ABC=43∘,find ∠BAC and∠ACB.
Side BC of triangle ABC is produced to D.
∴∠ACD=∠A+∠B
[Exterior angle property]
⇒128°=∠A+43°⇒∠A=128-43°⇒∠A=85°⇒∠BAC=85°
Also, in triangle ABC,
∠BAC+∠ABC+∠ACB=180° (Sum of the angles of a triangle)
⇒85°+43°+∠ACB=180°⇒128°+∠ACB=180°⇒∠ACB=52°