Tan(派/2+A)等于-cosa/sina,所以tana+tan(派/2+a)等于Sina/Cosa-cosa/sina等于sinasina-cosacosa除sinacosa,后一项同样把tana换成sina/cosa等于4sinacosa/cosacosa-sinasina,把sinacosa换成1/2sin2a,cosacosa-sinasina换成cos2a,最后解为-4/tan4a