This is a parallel chords on opposite sides of the centre question. You can recognise the
pattern because two chords, PQ and SR, are described as parallel and "separated by one of
the diameters" (meaning they sit on opposite sides of the centre), and the question asks
for the area of the quadrilateral PQRS formed by their endpoints. This always needs: the
distance of each chord from the centre, the length of each chord, and the distance between
the two chords.
Step 1: Use the 45 degree angle to find the distance from C to PQ.
Drop a perpendicular from C to PQ, meeting it at M. Then CM is perpendicular to PQ, so
triangle CMQ is right-angled at M, and angle CQM equals angle PQC, which is 45 degrees. In
a right triangle with a 45 degree angle, the two legs are equal, so CM = MQ.
By Pythagoras in triangle CMQ: CM^2 + MQ^2 = CQ^2 = (6*sqrt(2))^2 = 72.
Since CM = MQ, 2*CM^2 = 72, so CM^2 = 36 and CM = 6.
So the distance from C to PQ is d1 = 6.
Step 2: Use the given ratio to find the distance from C to SR.
The ratio of the two perpendicular distances is d1 : d2 = 3 : 2, so
d2 = (2/3) * 6 = 4.
Step 3: Find the half-lengths of both chords using the chord-distance formula.
Half-length of a chord = sqrt(r^2 - d^2), where r = 6*sqrt(2), so r^2 = 72.
For PQ: half-length = sqrt(72 - 36) = sqrt(36) = 6, so PQ = 12.
For SR: half-length = sqrt(72 - 16) = sqrt(56) = 2sqrt(14), so SR = 4sqrt(14).
Step 4: Find the height of trapezium PQRS.
Because PQ and SR lie on opposite sides of the centre (separated by a diameter), the
distance between the two chords equals the sum of their individual distances from the
centre: height h = d1 + d2 = 6 + 4 = 10.
Step 5: Compute the area of the trapezium.
PQRS is a trapezium with parallel sides PQ and SR and height h.
Area = (1/2) (PQ + SR) h = (1/2) (12 + 4sqrt(14)) * 10
= 5 (12 + 4sqrt(14)) = 60 + 20sqrt(14) = 20(3 + sqrt(14))
Answer: 20(3 + sqrt(14)) square cm, which is option C.
Common trap: students often add the two distances only when the chords lie on the SAME
side of the centre (where the actual gap would be d1 - d2). Here the chords are explicitly
on opposite sides of a diameter, so the distances must be added, not subtracted.