LHS

= tan 720° - cos 270° - sin 150° cos 120°

= tan (90° × 8 + 0°) – cos (90° × 3 + 0°) – sin (90° × 1 + 60°) cos (90° × 1 + 30°)

We know that when n is odd, cos → sin and sin → cos.

= tan 0° - sin 0° - cos 60° [-sin 30°]

= tan 0° - sin ° + cos 60° sin 30°

= 0 – 0 + 1/2 (1/2)

= 1/4

= RHS

Hence proved.