Page 137 - Math Smart - 7

Sum of angles In a triangle

We have learnt that a triangle Is a two-dimensional shape that has three straight
sides and three angles. We call the angles inside a triangle interior angles.

Lines AB, BC and AC make up triangle ABC {^ABQ.
Points A, B and C are the vertices of the triangle.

AABC, LACBand ABAC are the interior angles of AABC.

Let us find out what the sum of the angles in a triangle is.
Q Mark each angle in the triangles and cut them out.

50 mm 50 mm
5.5 cm

6 cm 78 mm

Q Use your protractor to measure the size of each interior angle.
Name the angles and write down the measurements below.

AA AB

^ Place the angles next to one another.

Do the angles fit exactly onto a straight line?

Q What is the sum of all the interior angles of each triangle?

♦Challenge! What triangle is this?

Conclusion
The sum of the interior angles of a triangle is