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