sin(-17π/6)=-sin（17π/6）=-sin（3π-π/6）=sin（-π/6）=-sin（π/6）=-1/2
sin（负6分之17π）=sin（4π-6分之17π）=sin（6分之7π）=sin（负6分之π）= -1/2
sin(-17π/6)=sin(-17π/6+2π）=sin(-5π/6)=-sin(5π/6)=-sin(π-5π/6)=-sin(π/6)=-1/2
