Question

Given: Quadrilateral DEFG is inscribed in circle P. Prove: m∠G+m∠E=180∘

Answer 1

The answer is below

Explanation:

Let lines be drawn from D to F (line DF) and from F to G (line FG) as shown in the diagram attached.

∠FDE = ∠FGE (angles in the same segment).

Also, ∠EFD = ∠EGD (angles in the same segment)

∠FDE + ∠EFD = ∠FGE + ∠EGD = ∠FGD

Adding ∠FED on both sides gives:

∠FDE + ∠EFD + ∠FED = ∠FGD + ∠FED

But ∠FDE + ∠EFD + ∠FED = 180° (sum of angles in a triangle)

Therefore ∠FGD + ∠FED = 180°

m∠G + m∠E = 180° (sum of opposite angles in a cyclic quadrilateral is 180°)