Geometry Angles Post 7

Angles Inside a Triangle
This is a common test type problem (you will definitely have to memorise this).  The gist of it is that all of the three corners of any triangle (remember that there are three types Equilateral, Isosceles, Right Angle and Scalene) you can form a straight line post #3.

Here is a physical proof of the idea that corners of triangles make straight lines...

The rule that we need is "Interior Angles of a Triangle sum to 180 degrees" (I'll accept inside angles of a triangle add to 180)

For Achieve you will need to be able to find the value of one corner (remember not drawn to scale)... problems like...

We can calculate the value of the missing corner (angle C).  We know all three must add up to 180.  So we use our calculator and put in...

                        180 - 38 - 85 = 57 (remember to use degree symbol)



These type of problems can be found on page 226 Exercise 14.13.