### Activity 2
#### Task 1
###### Step 1:
Draw a triangle *ABC* and cut out the three angles.
Step 2:
Rearrange the three angles to form a straight angle on a straight line.
So, the angle sum of a triangle is 180°.
Task 2
To investigate if this works for all triangles, repeat the above process
for four different triangles.
Task 3
Copy and complete the following statements:
a. The three angles of a triangle can be arranged to form a ………..
angle.
b. The sum of three angles in a triangle is ………..
Finding the Third Angle of a Triangle
If the measurements of two angles of a triangle are known, then the third
angle can be calculated.
Example 3
Calculate the size of the missing angle in the following triangle.
##### Solution:
Let the missing angle be *x*.
So, the missing angle is 80°.
Example 4
Find the values of the pronumerals *x* and *y* in the following
diagram:
##### Solution:
Example 5
Find the value of the pronumeral *x* in the following diagram:
##### Solution:
Example 6
Find the value of the pronumeral *x* in the following diagram:
##### Solution:
Example 7
Find the values of the pronumerals *x* and *y* in the following
diagram:
##### Solution:
Example 8
Find the value of the pronumeral *x *in the following diagram:
##### Solution:
Key Term
angle sum of a triangle |