The value of  tan⁡9∘−tan⁡27∘−tan⁡63∘+tan⁡81∘ is

We have  tan⁡9∘−tan⁡27∘−tan⁡63∘+tan⁡81∘=tan⁡9∘+tan⁡81∘−tan⁡27∘+tan⁡63∘=1cos⁡9∘cos⁡81∘−1cos⁡27∘cos⁡63∘=1sin⁡9∘cos⁡9∘−1sin⁡27∘cos⁡27∘=2sin⁡18∘−2sin⁡54∘=2sin⁡54∘−sin⁡18∘sin⁡54∘sin⁡18∘=22cos⁡36∘sin⁡18∘sin⁡18∘cos⁡36∘=4