document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=751462>Question 751462</A>: <I><SPAN STYLE=\"word-break: break-all;\"> (a) prove(i have done this part already)<BR>\n" );
document.write( "cos3a = 4cos^3 a - 3cosa\r<BR>\n" );
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document.write( "(b) Show that cos40 is a root of the equation 8x^3 - 6x +1 = 0\r<BR>\n" );
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document.write( "Need help with part (b) PLEASE </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #457249 by </B><A HREF=/tutors/aboutme.mpl?userid=Theo><B>Theo(13342)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Theo><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=Theo><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=457249\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> the second part sounds like it's a lot easier than the first part.\r<BR>\n" );
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document.write( "all you need to do is find the cosine of 40 degrees and replace x in the equation.\r<BR>\n" );
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document.write( "if the value of the equation comes out to be equal to 0, then cosine of 40 degrees is a root of the equation since the roots of the equation are when the value of y is equal to 0.\r<BR>\n" );
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document.write( "use your calculator to find cosine of 40 degrees.\r<BR>\n" );
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document.write( "that turns out to be equal to be equal to .766044443.\r<BR>\n" );
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document.write( "store that in your memory so as not to get rounding errors and use that stored result in place of x in the equation.\r<BR>\n" );
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document.write( "when you replace x in your equation with the stored value of .766044443, the result is 0 indicating that cosine of 40 degrees is a root of the equation.\r<BR>\n" );
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document.write( "alternately, you can graph your equation and find the roots (when the equation crosses the s-axis are the roots).\r<BR>\n" );
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document.write( "the graph of the equation actually crosses the x-axis in 3 places, and the third place (the rightmost intersection) is equal to the cosine of 40 degrees (.76604443).\r<BR>\n" );
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document.write( "the graph of the equation is shown below:\r<BR>\n" );
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document.write( "i drew a vertical line (well, almost vertical) at x = .766044443 to show you that the graph of the equation crosses the x-axis at that point.\r<BR>\n" );
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document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=graph%28600%2C600%2C-1%2C1%2C-5%2C5%2C8x%5E3-6x%2B1%2C300%28x-.766044443%29%29 ALIGN=MIDDLE  ALT=\"graph%28600%2C600%2C-1%2C1%2C-5%2C5%2C8x%5E3-6x%2B1%2C300%28x-.766044443%29%29\"   DISABLED_style= \"max-width:90%; height:auto;\" >\r<BR>\n" );
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