Or search by topic
$P$, $Q$ and $R$ are points on the circumference of a circle of radius 4cm. $\angle PQR=45^o$. What is the length of chord $PR$?
If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.
The area of a regular pentagon looks about twice as a big as the pentangle star drawn within it. Is it?
Prove that the internal angle bisectors of a triangle will never be perpendicular to each other.