tanx=-√2
→1/cos^2 x = 1 + tan^2 x = 3;
由于-pi/2sin(x-pi/6)
=sinx·cos(pi/6) - cosx·sin(pi/6)
=√3·sinx /2 - cosx /2
=cosx(√3·tanx -1)/2
=(-√2 - √3/3)/2
= -√2/2 - √3/6