document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1205673>Question 1205673</A>: <I><SPAN STYLE=\"word-break: break-all;\"> the distance between the centers of the two circles is 13 cm. If their radii are 5cm and 8cm, how long is their common external tangent segment?\r<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #842640 by </B><A HREF=/tutors/aboutme.mpl?userid=greenestamps><B>greenestamps(13200)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=greenestamps><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=greenestamps><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=842640\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <br><BR>\n" );
document.write( "Let A be the center of the circle with radius 5cm and B be the center of the circle with radius 8cm.<br><BR>\n" );
document.write( "Since the distance between the centers is 13cm, the two circles are tangent to each other.<br><BR>\n" );
document.write( "Draw the common external tangent CD, with C and D being the points of tangency with circles A and B respectively.  The radii AC and BD are both perpendicular to the tangent CD.<br><BR>\n" );
document.write( "Let point E be on radius BD so that AE is parallel to the tangent CD.  ACDE is then a rectangle, with one dimension 5 cm and the other dimension equal to the length of the common external tangent.<br><BR>\n" );
document.write( "Use the Pythagorean Theorem on right triangle ABE to find the length of the other dimension of the rectangle and thus the length of the external common tangent.<br><BR>\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x%5E2%2B3%5E2=13%5E2 ALIGN=MIDDLE  ALT=\"x%5E2%2B3%5E2=13%5E2\"   DISABLED_style= \"max-width:90%; height:auto;\" ><BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=x=sqrt%28160%29=4%2Asqrt%2810%29 ALIGN=MIDDLE  ALT=\"x=sqrt%28160%29=4%2Asqrt%2810%29\"   DISABLED_style= \"max-width:90%; height:auto;\" ><br><BR>\n" );
document.write( "ANSWER: <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=4%2Asqrt%2810%29cm ALIGN=MIDDLE  ALT=\"4%2Asqrt%2810%29cm\"   DISABLED_style= \"max-width:90%; height:auto;\" ><br><BR>\n" );
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