In the figure below, ABC is a triangle in which ∠BAC = 30°. Show that BC is equal to radius of the circumcircle where centre is O.
Two chords AB and CD of lengths 5 cm and 11 cm respectively of a circle are parallel to each other and are on opposite sides of its centre. If the distance between AB and CD is 6 cm, find the radius of the circle.
The lengths of two parallel chords of a circle are 6 cm and 8 cm. If the smaller chord is at distance 4 cm from the centre, what is the distance of the other chord from the centre?
∵ OM 1 AB
∴ is the mid-point of AB.
| The perpendicular from the centre of a circle to a chord bisects the chord
∵ ON ⊥ CD
∴ N is the mid-point of CD.
| The perpendicular from the centre of a circle to a chord bisects the chord
In triangle OMB,
OB2 = OM2 + MB2
| By Pythagoras Theorem
= (4)2 + (3)2
= 16 + 9 = 25
In right triangle OND,
OD2 + ON2 + ND2
| By Pythagoras Theorem
(5)2 = ON2 + ND2
25 = ON2 + 16
ON2 = 25 - 16
ON2 = 9
Hence, the distance of the chord from the centre is 3 cm.
Case II. When the two chords are on the opposite sides of the centre
As in case I
ON = 3 cm.
Let the vertex of an angle ABC be located outside a circle and let the sides of the angle intersect equal chords AD and CE with the circle. Prove that ∠ABC is equal to half the difference of the angles subtended by the chords AC and DE at the centre.
AC and BD are chords of a circle which bisect each other. Prove that (i) AC and BD are diameters, (ii) ABCD is a rectangle.