cos2a/(1-2tana*cos^2a)
=cos2a/(1-2sinacosa)
=(cos²a-sin²a)/(cos²a-2sinacosa+sin²a)
=(cosa-sina)(cosa+sina)/(cosa-sina)²
=(cosa+sina)/(cosa-sina)
=√2(sinacosπ/4+cosasinπ/4)/[√2(cosacosπ/4-sinasinπ/4)]
=sin(a+π/4)/cos(a+π/4)
=tan(a+π/4)
cos2a/(1-2tana*cos^2a)
=cos2a/(1-2sinacosa)
=(cos²a-sin²a)/(cos²a-2sinacosa+sin²a)
=(cosa-sina)(cosa+sina)/(cosa-sina)²
=(cosa+sina)/(cosa-sina)
=√2(sinacosπ/4+cosasinπ/4)/[√2(cosacosπ/4-sinasinπ/4)]
=sin(a+π/4)/cos(a+π/4)
=tan(a+π/4)