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Question
The length of the direct common tangent to two circles of radii 12cm and 4cm is 15cm. calculate the distance between their centres.
Solution
R1 = 4cm, R2 = 12cm
PQ = l5 cm
AB2 = PQ2 + (R2 - R1)2
=> AB2 = 152 + (12 - 4)2
=> AB2 = 225 + 64
=>AB2 = 289
=> AB = 17cm
The diameter between the centre is 17cm
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