Question

已知sin（45°+a）sin（45°-a）=-1/4,0°

Answer 1

1,sin(45+a)sin(45-a)

=sin(45+a)cos(45+a)

=1/2sin(90+2a)

=1/2cos(2a)

=-1/4

解得cos(2a)=-1/2;a=60

2,sin(a+10)(1-(根号3)tan(a-10))

=sin70*(1-(根号3)*tan50)

=cos20/cos50*(cos50-(根号3)*sin50)

=2cos20/sin40*(1/2*cos50-(根号3)/2*sin50)

=1/sin20*sin(30-50)

=1/sin20*(-sin20)

=-1;