a) The size of angle ABC is equal to 120 degrees.
b) The size of reflex angle CBD is equal to 240 degrees.
A semi-circle always has a measure of 180°. This ultimately implies that, a protractor measures 180°. In order to read an angle measure by using a protractor, we would have to align the horizontal side with 0° and read the angle for the second side.
Part a.
By critically observing the image of the protractor, we can logically deduce that the specific measure of angle ABC is 120 degrees because the line lies exactly at 120 and it represents an obtuse angle because it is greater than 90 degrees, but less than 180;
Angle ABC = 120°, Obtuse angle.
Part b.
Since a reflex angle measures more than 180 degrees, but less than 360 degrees, we would have to subtract the measure of angle ABC from 360 as follows;
Reflex angle CBD = 360 degrees - 120 degrees
Reflex angle CBD = 240 degrees.
Complete Question:
a) What is the size of angle ABC?
b) Use your answer to part a) to work out the size of reflex angle CBD.
Give your answers to the nearest degree.