Question

prove that sum of interior angle of triangle is 180 degree

Answer 1

let a1, a2 and a3 be the three sides of triangle
/_1 +/_2 +/_3=180 (angle sum property

or
when we take out the three sides of a triangle, it forms a straight angle
like:-
image is above

Answer 2

Answer:

Step-by-step explanation:

Given: ABC is a triangle.

To Prove : <1 +<2+<3=180•

Construction : Through A, draw a line DE parallel to BC.

Proof: DE//BC and AB is the transversal.

Therefore, <1=<4.............(I) [alt. Int. <s]

Again, DE//BC and AC is the transversal.

Therefore, <2=<5...............(2) [alt. Int. <s]

Therefore, <1+<2=<4+<5

[adding the corresponding sides of (1) and (2)] .

So, <1+<2+<3=<4+<5+<3. [adding <3 both sides..]

But, <4+<5+<3=<DAE=180 [ <DAE is a straight angle]

Therefore, <1+<2+<3=180.

Hence, the sum of the angles of a triangle is 180.