document.write( "Question 811734: cos u − cos 2u = 0 \n" ); document.write( "
Algebra.Com's Answer #488930 by lwsshak3(11628)\"\" \"About 
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For interval[0,2π]
\n" ); document.write( "cos u − cos 2u = 0
\n" ); document.write( "cos(u)-(cos^2(u)-sin^2(u))=0
\n" ); document.write( "cos(u)-cos^2(u)+sin^2(u)=0
\n" ); document.write( "cos(u)-cos^2(u)+1-cos^2(u)=0
\n" ); document.write( "2cos^2(u)-cos(u)-1=0
\n" ); document.write( "(2cos(u)+1)(cos(u)-1)=0
\n" ); document.write( "..
\n" ); document.write( "2cos(u)+1=0
\n" ); document.write( "cos(u)=-1/2
\n" ); document.write( "u=2π/3,4π/3
\n" ); document.write( "or
\n" ); document.write( "cos(u)+1=0
\n" ); document.write( "cos(u)=-1
\n" ); document.write( "u=π\r
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "
\n" );