document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1209346>Question 1209346</A>: <I><SPAN STYLE=\"word-break: break-all;\"> David wants to add one more dot to the diagram below so that the four dots form the four vertices of a parallelogram.  If A = (3,4), B = (4,-1), C = (6,8), then where should D be to form parallelogram ABCD? </SPAN>\n" );
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document.write( "Answer: <font color=red>(5,13)</font>\r<BR>\n" );
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document.write( "Explanation:\r<BR>\n" );
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document.write( "To go from B to C we go up 9 and right 2<BR>\n" );
document.write( "Start at point A(3,4) and go up 9 and right 2 so you arrive at <font color=red>(5,13)</font> <BR>\n" );
document.write( "This is where D should be placed to get parallelogram ABCD.\r<BR>\n" );
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document.write( "Technically there are 2 other spots D could go if we didn't care about the order of ABCD. But I'll assume that the order matters.\r<BR>\n" );
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document.write( "To prove that ABCD is a parallelogram, you need to show that<BR>\n" );
document.write( "slopeAB = slopeCD<BR>\n" );
document.write( "slopeBC = slopeAD<BR>\n" );
document.write( "I'll let the student do these verifications. The slope formula is <BR>\n" );
document.write( "m = (y2-y1)/(x2-x1)<BR>\n" );
document.write( "or you can use the rise/run concept. \r<BR>\n" );
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