document.write( "Question 1074109: Let B, C, and D be points on a circle. Let BC and the tangent to the circle at D intersect at A. If AB = 4, AD = 8, and AC is perpendicular to AD, then find CD.\r
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Algebra.Com's Answer #688839 by ikleyn(52778)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "The key to the solution of the problem is this theorem\r\n" );
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document.write( "     Theorem\r\n" );
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document.write( "     If a tangent and a secant lines are released from a point outside a circle, \r\n" );
document.write( "     then the product of the measures of the secant and its external part is equal to the square of the tangent segment.\r\n" );
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document.write( "For the proof, see the lesson\r\n" );
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document.write( "    - Metric relations for a tangent and a secant lines released from a point outside a circle\r\n" );
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document.write( "in this site.\r\n" );
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document.write( "Using the theorem, you can find the length of the secant AC:  |AC| = \"%28abs%28AD%29%5E2%29%2Fabs%28AB%29\" = \"8%5E2%2F4\" = \"64%2F4\" = 16 units.\r\n" );
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document.write( "Then |CD| = \"sqrt%2816%5E2+%2B+8%5E2%29\" = \"sqrt%28320%29\" = \"8%2Asqrt%285%29\".\r\n" );
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\n" ); document.write( "\n" ); document.write( "Also,  you have this free of charge online textbook on Geometry\r
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\n" ); document.write( "\n" ); document.write( "The referred lessons are the part if this textbook under the topic
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