document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=828946>Question 828946</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Find a linear function f(x) = mx + b such that m is positive and (f(f(x))= 9x + 4.\r<BR>\n" );
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document.write( "The answer is 3x + 1 and I can find this by trial and error. What I want to know is how to reach this answer mathematically.\r<BR>\n" );
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document.write( "I've tried to do it this way: 9x + 4 = m(mx + b) + b = m^2(x) + bm + b but then I got stuck because I have too many unknowns to solve by the quadratic equation.\r<BR>\n" );
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document.write( "Could you please explain this to me?\r<BR>\n" );
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document.write( "Thanks in advance </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #499580 by </B><A HREF=/tutors/aboutme.mpl?userid=oscargut><B>oscargut(2103)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=oscargut><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=oscargut><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=499580\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> you started right\r<BR>\n" );
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document.write( "then you must solve\r<BR>\n" );
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document.write( "m^2 =9<BR>\n" );
document.write( "and b(m+1)=4\r<BR>\n" );
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document.write( "you can ask me more at\r<BR>\n" );
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document.write( "mthman@gmail.com\r<BR>\n" );
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document.write( "thanks </SPAN>\n" );
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