document.write( "Question 821921: csc theta = sqrt(31). What would cos(2theta) equal? \n" ); document.write( "

Algebra.Com's Answer #494594 by lwsshak3(11628) $\"\"$ $\"About$

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csc theta = sqrt(31). What would cos(2theta) equal?
\n" ); document.write( "cscx=√31
\n" ); document.write( "sinx=1/√31=√31/31
\n" ); document.write( "Identity:cos2x=1-2sin^2x)=1-2*31/961)=1-(62/961)=899/961
\n" ); document.write( "..
\n" ); document.write( "calculator check:
\n" ); document.write( "sinx=√31/31
\n" ); document.write( "x≈10.35˚
\n" ); document.write( "2x≈20.69˚
\n" ); document.write( "cos2x=cos(20.69)≈0.935..
\n" ); document.write( "exact value as calculated=899/961≈0.935.. \n" ); document.write( "

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