Question

prove that sum of the three angles of a triangle is 180°

Answer 1

Refer the attachment for figure.


Construct a triangle ABC and name the :-
angle A = x,
angle B = y
angle c = z


Now construct a line parallel to BC crossing A. Name. the line as ED (refer the attachment)

Now you will find that,

Angle DAB = y (alternate angle)

and, angle EAC = z (alternate angle)

and, angle DAB, angle A, angle EAC lies on a line ED.

We know that the sum of angles lying on a line is 180°

=> angle DAB + angle A + angle EAC = 180°

but, angle DAB = y, angle A = x and angle EAC = z

=> x + y + z = 180°

And x, y and z are the angles of a triangle

=> sum of angles of a triangle = 180°

Hence Proved :)

Answer 2

Answer:

hope it helps a lot....