document.write( "Question 734294: Prove: sec(alpha + beta)= cos(alpha)cos(beta)+sin(alpha)sin(beta)/cos^2(alpha)-sin^2(beta)\r \n" );
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document.write( "I know that sec=1/cos so I changed sec(alpha+beta) to 1/cos(alpha+beta) which gave me: \n" );
document.write( "a=alpha b=beta\r \n" );
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document.write( "1/cos(a)cos(b)-sin(a)sin(b)\r \n" );
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document.write( "not sure what the next step is. thank you \n" );
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