In Δ ABC, D,E and F are taken on AB, AC and BC respectively, so that EF=CF and DF=BF. If ∠A=40∘, then find ∠DFE?
Option (a)
Take DBF = a∘ and ECF = b∘.
40 + a∘ + b∘ = 180 ⇒ a∘ + b∘= 140
DFB + EFC + DFE = 180 ⇒ 180 – 2a∘ + 180 – 2b∘ + DFE = 180 ⇒ 180∘ – 2(a + b) = - DFE
DFE = 280 – 180 = 100∘