document.write( "Question 1057159: If cos54 = t, determine cos144 in terms of t \n" ); document.write( "

Algebra.Com's Answer #672236 by ikleyn(52898) $\"\"$ $\"About$

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\n" ); document.write( "If cos(54°) = t, determine cos(144°) in terms of t
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document.write( "Notice that  144° = 90° + 54°.\r\n" );
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document.write( "Based on it, I will find cos(144°) in one steps.\r\n" );
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document.write( "cos(144°) = cos(90°+54°) =  ( apply the formula cos(a+b) = cos(a)*cos(b) - sin(a)*sin(b) ) = \r\n" );
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document.write( "            cos(90°)*cos(54°) - sin(90°)*sin(54°) =  = .\r\n" );
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\n" ); document.write( "\n" ); document.write( "Solved. The answer is cos(144°) = $\"-sqrt%281-t%5E2%29\"$ .\r
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