cos2a/(sinacosπ/4-cosasinπ/4)=-√2/2
(cos²a-sin²a)/(sina*√2/2-cosa**√2/2)=-√2/2
(cosa-sina)(cosa+sina)/[-√2/2(cosa-sina)]=-√2/2
cosa+sina=1/2
cos2a/(sinacosπ/4-cosasinπ/4)=-√2/2
(cos²a-sin²a)/(sina*√2/2-cosa**√2/2)=-√2/2
(cosa-sina)(cosa+sina)/[-√2/2(cosa-sina)]=-√2/2
cosa+sina=1/2