cos 510∘=cos(330∘+150∘)=cos150∘=cos(180∘−30∘)=cos30∘
cos 510∘=cos(540−30)=−cos 30
cos 330∘=cos(360∘−30)=+cos 30
sin 390∘=sin(360+30)=sin30∘
cos 120∘=cos(90+30)=−sin30∘
So the given expression changes to - cos230∘−sin230∘
= −(sin230+cos230)
= - 1