Question

已知tana/tana-1=-1,求下列各式的值（1）sina-3cosa/sina+cosa(2)sin²a

Answer 1

sina/cosa/(sina/cosa-cosa/cosa)=-1

sina/cosa= -(sina-cosa)/cosa

sina=-sina+cosa

2sina=cosa

sina-3cosa=sina-6sina= -5sina

sina+cosa=sina+2sina= 3sina

sina-3cosa/sina+cosa= - 5/3

sin²a+sinacosa+3cos²a

=sin²a+cos²a+2sina*sina+2cos²a

=1+2

=3