document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=191164>Question 191164</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Please help me solve this substitution problem. <BR>\n" );
document.write( "3(x-y)=15<BR>\n" );
document.write( "2x+y=7<BR>\n" );
document.write( "The question I have is does it matter which equation I use as the substitution? I used the 2nd equation and came up with a different answer than with the first. <BR>\n" );
document.write( "First solution:<BR>\n" );
document.write( "3(x-y)=15<BR>\n" );
document.write( "2x+y=7 y=7-2x\r<BR>\n" );
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document.write( "3(x-7-2x)=15<BR>\n" );
document.write( "3x-21-6x=15<BR>\n" );
document.write( "-3x=36<BR>\n" );
document.write( "x=-12<BR>\n" );
document.write( "y=7-2x<BR>\n" );
document.write( "y=7-2(-12)<BR>\n" );
document.write( "y=31\r<BR>\n" );
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document.write( "Second solution:<BR>\n" );
document.write( "3(x-y)=15 3x-3y=15<BR>\n" );
document.write( "2x+y=7       3x=15+3y<BR>\n" );
document.write( "              x=5+y\r<BR>\n" );
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document.write( "2(5+y)+y=7<BR>\n" );
document.write( "10+2y+y=7<BR>\n" );
document.write( "3y=-3<BR>\n" );
document.write( "y=-1<BR>\n" );
document.write( "x=5+y<BR>\n" );
document.write( "x=5+-1<BR>\n" );
document.write( "x=4<BR>\n" );
document.write( " <BR>\n" );
document.write( "which is correct and how do I know which equation to start with on these types of problems?\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 #144943 by </B><A HREF=/tutors/aboutme.mpl?userid=MathTherapy><B>MathTherapy(10552)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=MathTherapy><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=MathTherapy><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=144943\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> 3(x - y)= 15 <BR>\n" );
document.write( "2x + y = 7\r<BR>\n" );
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document.write( "2x + y  = 7<BR>\n" );
document.write( "y = 7 - 2x <BR>\n" );
document.write( "Substituting this value for y in eq. (i) gives us: <BR>\n" );
document.write( "3{x-(7-2x)} = 15<BR>\n" );
document.write( "3(x – 7 + 2x) = 15<BR>\n" );
document.write( "3x – 21 + 6x = 15<BR>\n" );
document.write( "9x  =  36<BR>\n" );
document.write( "x  =  4\r<BR>\n" );
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document.write( "Substitute this value for x in eq. (ii) 2x + y = 7. This give us:<BR>\n" );
document.write( "2(4) + y = 7<BR>\n" );
document.write( "y = - 1\r<BR>\n" );
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document.write( "You made an error when substituting the value of y (7 – 2x) into the 1st equation (see above). As seen, either equation can be substituted in order to find the values of x and y. So, the answer is (4, - 1).<BR>\n" );
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