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The radii of two circles are 4 cm and 7 cm and the distance between their centres is 12 cm. Find the length of the direct common tangent to the circles. |
$3\sqrt{6}$ cm $2\sqrt{6}$ cm $2\sqrt{15}$ cm $3\sqrt{15}$ cm |
$3\sqrt{15}$ cm |
Length of direct common tangent = \(\sqrt {d² - ( R - r )² }\) = \(\sqrt {12² - ( 7 - 4 )² }\) = \(\sqrt {144 - 9 }\) = \(\sqrt {135 }\) = 3\(\sqrt {15 }\) cm |
