document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1106055>Question 1106055</A>: <I><SPAN STYLE=\"word-break: break-all;\"> If cos&#952; = 4/5 and &#952; is an acute angle, find the exact value of cos(&#952;-45°).\r<BR>\n" );
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document.write( "Please show me how to solve other problems like this, I'm trying to learn Algebra 2 by myself and my textbook doesn't have enough examples. </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #720972 by </B><A HREF=/tutors/aboutme.mpl?userid=rothauserc><B>rothauserc(4718)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=rothauserc><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=rothauserc><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=720972\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> theta is acute, then theta < 90 degrees<BR>\n" );
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document.write( "cos theta = 4/5<BR>\n" );
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document.write( "use the inverse trig function to find theta<BR>\n" );
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document.write( "cos^(-1) (4/5) = 36.87 degrees<BR>\n" );
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document.write( "36.87 - 45 = -8.13<BR>\n" );
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document.write( "cos(-8.13) = 0.99<BR>\n" );
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document.write( "Note negative angles are measured clockwise, so instead of taking the cosine of -8.13, we could haave taken the cosine of (360 - 8.13) and get the same answer<BR>\n" );
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document.write( "if your teacher does not want you to use inverse trig functions, you can use trig identities<BR>\n" );
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document.write( "sin^2 theta + cos^2 theta = 1<BR>\n" );
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document.write( "sin^2 theta + (4/5)^2 = 1<BR>\n" );
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document.write( "sin^2 theta = 1 - 16/25 = 9/25<BR>\n" );
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document.write( "sin theta = 3/5<BR>\n" );
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document.write( "cos(theta-45) = cos theta * cos 45 + sin theta * sin 45<BR>\n" );
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document.write( "cos(theta-45) = (4/5) * 0.7071 + (3/5) * 0.7071 = 0.99<BR>\n" );
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