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Question
Calculate the length of direct common tangent to two circles of radii 3cm and Bern with their centres 13cm apart.
Solution
To find: PQ
R1 = 3cm, R2 = 8cm
AB= 13cm
PQ2 = AB2 -(R2 -R1)2
⇒ PQ2 = 132 - ( 8 - 3)2
⇒ PQ2 = 169 - 25
⇒ PQ2 = 144
⇒ PQ = 12cm
Length of direct common tangent is 12cm
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