Question

how to prove the sum of four angels in a quadrilateral is 360​

Answer 1

Answer: diagonally draw a line to quadrilateral

now there will be two triangles

we know that sum of all angles in triangle is 180 degree

now there are two triangles in quadrilateral

one have 180 degree and second have 180 degree

adding both 360

hence proved

Step-by-step explanation:

Answer 2

Answer:

Proof: Let ABCD be a quadrilateral. Join AC.

Clearly, ∠1 + ∠2 = ∠A ...... (i)

And, ∠3 + ∠4 = ∠C ...... (ii)

We know that the sum of the angles of a triangle is 180°.

From ∆ACD, we have

∠1 + ∠3 + ∠D = 180° (Angle sum property of triangle)

Adding the angles on either side, we get;

∠2 + ∠4 + ∠B + ∠1 + ∠3 + ∠D = 360°

⇒ (∠1 + ∠2) + ∠B + (∠3 + ∠4) + ∠D = 360°

⇒ ∠A + ∠B + ∠C + ∠D = 360° [using (i) and (ii)].

Hence, the sum of all the four angles of a quadrilateral is 360°.