Question

cos 510° cos330° + sin390° cos(-120°)​

Answer 1

Step-by-step explanation:

cos510cos330+sin390cos120

                We have

                cos510=cos(360+150)=cos150

                =cos(180−300)

                =−cos30

                cos330=cos(360−30)=cos30

                sin390=sin(360+30)=sin30

                &cos120=cos(90+30)=−sin300

                ∴LHS=−cos30⋅cos30+sin3θ(−sin30)

                =−(cos230+sin230)

                =−1