Theorem 4

Question 1

Theorem

Answer 1

The angles of any triangle add up to 180°

Question 2

Given

Answer 2

The triangle abc with angles marked with 123

Question 3

Construction

Answer 3

Draw a line L through A parallel to BC, mark these angles 4 and 5

Question 4

Required to prove

Answer 4

|<1| + |<2| +|<3| = 180°

Question 5

Proof

Answer 5

|<2| = |<4| and |<3| = |<5| …… alternate angles

|<1| + |<4| + |<5| = 180°

For <4 and <5 sub in <2 and <3

|<1| + |<2| + |<3| = 180°