On a plane figure when three lines intersect each other at their last end is called a triangle. The end place where lines intersect to other lines, makes a corner. These corners makes an angle. In a triangle there are only three corners and three angles. The sum of all the three angles in a triangle is 180°. There are 3 types of triangles:
1) Acute angled triangle |
All the angles in a acute angled triangle are <90°. |
2) Right angled triangle |
One of the angles in a right angled triangle is 90° |
3) Obtuse angled triangle |
One of the angles in an obtuse angled triangle is >90° |
Example 1: Two angles of a triangle measures 59° and 85°. Find the remaining angle?
| Answer: |
Sum of all the angles in a triangle is 180°. 59° + 85° + x = 180° 144° + x = 180° x = 36° |
Hence the third angle is 36°.
Example 2: The three angles of a triangle measure (3x) °, (4x – 8) °, (3x – 2) °. Find x and all the three angles.
| Answer: |
3x + 4x – 8 + 3x – 2 = 180 10x – 10 = 180 10x = 190 x = 19° |
First angle = 3x = 3(19) = 57°
| Second angle |
= 4x – 8
= 4(19) – 8
= 76 – 8
= 68°
|
| Third angle |
= 3x – 2
= 3(19) – 2
= 57 – 2
= 55°
|
