Q: Draw a circle of radius 4 cm. Construct a pair of tangents to it, the angle between which is $60^{\circ}$. Also, justify the construction. Measure the distance between the centre of the circle and the point of intersection of tangents.
Solution
Steps of construction:
1. Construct a circle with $O$ as a centre and a 4 cm radius
2. Construct any diameter $A O B$
3. Construct an angle $\angle A O P=600$ where $O P$ is the radius which intersect the circle at the point $P$
4. Construct $P Q$ perpendicular to $O P$ and $B E$ perpendicular to $O B$
$P Q$ and $B E$ intersect at the point $R$
5. $R P$ and $R B$ are the required tangents
6. The measurement of $O R$ is 8 cm
Justification:
PR is the tangent to a circle
$$
\angle O P Q=900
$$
$B R$ is the tangent to a circle
$$
\angle O B R=900
$$
So we get
$$
\angle P O B=180-60=1200
$$
In BOPR
$$
\angle B R P=360-(120+90+90)=600
$$
Therefore, the distance between the centre of the circle and the point of intersection of tangents is 8 cm.