Two circles of radii 5.5 cm and 4.2 cm touch each other externally. Find the distance between their centres.

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9.7 Explanation: Let the two circles having centres P and R touch each other externally at point Q. Here, PQ = 5.5 cm, QR = 4.2 cm The two circles touch each other externally. ...(P–Q–R) If the circles touch each other externally, distance between their centres is equal to the sum of their radii. ∴ By theorem of touching circles, ∴ PR = PQ + QR ∴ PR = 5.5 + 4.2 ∴ PR = 9.7 cm ∴ The distance between the centres of the circles is 9.7 cm.

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