Prepare an activity about sum of three angle is 180 degree
Answers
Answer:
Above, you probably made a guess that the sum of the angles in a triangle is 180°.
That is true. Here is a proof for it. Proof means that we use already established principles to prove
that some new statement is always true. See if you can understand the reasoning in this proof!
We draw a line parallel to AB that passes
through point C.
Angles C and C' are vertical angles,
therefore ∠C = ∠C'.
Angles B and B' are corresponding angles,
therefore ∠B = ∠B'.
Angles A and A' are corresponding angles, therefore ∠A = ∠A'.
So, the angle sum ∠A + ∠B + ∠C is equal to the angle sum ∠A' + ∠B' + ∠C'.
The three angles A', B', and C' form together a straight angle (they are along the line l).
So, their angle sum is 180°. But then the angle sum ∠A + ∠B + ∠C must also be 180°.
Step-by-step explanation: