ANGLES IN A TRIANGLE

Triangles are the simplest polygons with three sides and three angles. The sum of the three angles of a triangle is equal to 180 degrees.

Find the value of x in the figure below.

This question can be tackled by using algebra.

METHOD 1

100° + 3x + x = 180° 100° + 4x = 180° 4x = 180° — 100° 4x = 80° x = 80° 4 x = 20°

x = 20° 3x = 3 x 20° = 60°

Steps involved :1. Add all the angles 2. Add the unknown values (x, 3x)

and the known value (100° )3. Bring the known value to the

other side and subtract from 180°

4. Divide the value left by 4 ( total of the unknown angles to find the value of x.)

5. When x is found, then the value of the unknown angles can be found by substitution.

METHOD 2

This method is almost the same with the first method. The only difference is in the fourth step. Instead of dividing 80 by 4, here it is changed into fraction of

100°+ 3x + x = 180°

100° + 4x = 180° 4x = 80° x = x = 20°

x = 20° 3x = 3 x 20° = 60°

480

20 °

480

Another question to try on!

Find the value of x ?Mathematics Paper 1, 1995

Check Answer

73°

64° x

Working and answer

64° + 73° + x = 180°

137° + x = 180°

x = 180° ― 137°

x = 43°