Circle in a semicircle

Imagine cutting out a circle which is just contained inside a semicircle. What fraction of the semi-circle will remain?
Age
14 to 16
Challenge level
filled star filled star empty star
Exploring and noticing Working systematically Conjecturing and generalising Visualising and representing Reasoning, convincing and proving
Being curious Being resourceful Being resilient Being collaborative

Problem



The diagram shows a semi-circle containing a circle which touches the circumference of the semicircle and goes through its centre. What fraction of the semicircle is shaded?

Circle in a Semicircle

 

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.