In figure, ABCD is a square and ∠DEC is an equilateral triangle. Prove that
(i) ∆ADE ≅ ∆BCE
(ii) AE = BE
(iii) ∠DAE = 15°
Given: In ∆ABC, AB = AC, ∠A = 36°. The internal bisector of ∠C meets AB at D.
To Prove: AD = DC
Proof: In ∆ABC,
∵ AB = AC
∴ ∠ABC = ∠ACB ...(1)
| Angles opposite to equal sides of a triangle are equal
Also, ∠BAC + ∠ABC + ∠ACB = 180°
| Angle sum property of a triangle
⇒ 360° + ∠ABC + ∠ACB = 180°
⇒ ∠ABC + ∠ACB = 144° ...(2)
From (1) and (2),
Now, ∵ CD bisects ∠ACB
Again, In ∆ACD,
∠ACD = ∠CAD (= 36°)
∴ AD = DC
| Sides opposite to equal angles of a triangle are equal