Match the two columns:
Column−IColumn−II(A) The radius of a circle is 8 cm and(p) 23 cm the length of one of its chords is 12 cm. The distance of the chord form the centre is (B) Two parallel chords of length 30 cm (q) 5.196cm and 16 cm are drawn on the opposite sides of the centre of a circle of radius 17 cm. The distance between the chords is(C) The length of a chords which is at a distance of(r) 5.291 cm 4 cm from the centre of the circle of radius 6 cm is(D) An equilateral triangle of side 9 cm is inscribed (s) 8.94 cm in a circle. The radius of the circle is Choose the correct option:
A-r; B-p; C-s; D-q
(b) (A)→r;(B)→p;(C)→s;(D)→q
(A) Let PQ be the chord of a circle with centre O and radius 8 cm such that PQ = 12 cm. From O, draw OL⊥PQ. Join OP. Since the perpendicular from the centre of a circle to a chord bisects the chord. PL=LQ=12PQ=6 cm In right triangle OLP, we have
OP2=OL2+PL2
⇒82=OL2+62⇒OL2=82−62⇒OL2=82−62=64−36=28⇒OL=√28=5.291cm
Hence, the distance of the chord from the centre is 5.291 cm.
(B) We know that the perpendicular from the centre of a circle to a chord bisects the chord.
In Δ PLO, PL = 15cm and PO = 17cm
By pythagoras theoram,
PO2 = PL2 + LO2
LO2 = 152 - 172
LO2 = 225 - 289
LO = 8cm
Similarly MO = 15cm
Therefore, LM = 15 + 8 = 23cm
(C) Let PQ be a chord of a circle with centre O and radius 6 cm. Draw OL⊥PQ. Join OP then OL = 4 cm and OP = 6 cm.
From the right-angled ΔOPL, we have
OP2=OL2+PL2⇒PL2=OP2−OL2⇒PL2=62−42=36−16=20⇒PL2=4.472cm
Since the perpendicular from the centre of the circle to a chord bisects the chord, we have
PQ=2×PL=2×4.472=8.94 cm
(D) Let Δ PQR be an equilateral triangle of side 9 cm. Let PS be one of its medians. Then PS⊥QR and QS = 4.5 cm
PS=√PQ2−QS2
=√92−(92)2cm=9√32cm
In an equilateral triangle, the centroid and circumcenter coincide and PG:PS = 2 : 3
∴ Radius=PG=23PS=23×9√32
=3√3=5.196cm