Question

Please answer . The first to give the answer with proper explanation will be marked as brainliest....​

Answer 1

draw a line xy parallel to ab at vertex b,

∠cab = ∠abx  (co-interior angles)

∠acb = ∠cby (co-interior angles)

∠abc + ∠cby + ∠abx =180°

therefore, ∠cab + ∠acb + ∠abc =180°

angle sum of a triangle = 180°

sum of angles of two triangles = 180° +180° = 360°

therefore angle sum of quadrilateral = 360°