Answer with explanation:
Given:
In Δ DEF, ∠3=∠4.
To prove:→ DE=E F
Proof:
1. ∠3=∠4------[Given]
2. →∠1 and ∠ 3 are Supplementary to each other.
(a)⇒∠1 + ∠ 3=180°
→∠2 and ∠ 4 are also Supplementary to each other.
(b)⇒∠2 + ∠ 4=180°
--------------------[Exterior sides in opposite rays]
3. From 1 , a and b
⇒∠ 1 = ∠ 2-------[Two Angles Supplementary to equal Angles are equal to each other]
4.
If two angles of a Triangle are equal , then side opposite to these angles are equal.