document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=533724>Question 533724</A>: <I><SPAN STYLE=\"word-break: break-all;\">  </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #351134 by </B><A HREF=/tutors/aboutme.mpl?userid=fcabanski><B>fcabanski(1391)</B></A><img src=\"/images/stars/stars-12.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=fcabanski><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/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=351134\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> What is a, if f(a)=8, and f(x)=2^-x\r<BR>\n" );
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document.write( "Substitute a for x in the second equation:  f(a) = 2^-a\r<BR>\n" );
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document.write( "Set it equal to the solution for f(a)\r<BR>\n" );
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document.write( "2^-a = 8\r<BR>\n" );
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document.write( "Recall that with exponents, that if x^y = x^z then y=z.  Often to solve such problems we have to express the constant (in this case 8) in terms of the same base as the term with the exponent (in this case 2).\r<BR>\n" );
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document.write( "8 = 2^3.  So we can rewrite this equation as:\r<BR>\n" );
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document.write( "2^-a = 2^3\r<BR>\n" );
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document.write( "Recall that with exponents, that if x^y = x^z then y=z.\r<BR>\n" );
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document.write( "-a = 3 divide both sides by -1 so   a=-3 </SPAN>\n" );
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