Prove that: $\tan^6 20° - 33\tan^4 20° + 27\tan^2 20°=3$

My Attempt:

$$L.H.S=\tan^6 20 - 33\tan^4 20 + 27\tan^2 20°$$
$$=\tan^2 20°(\tan^4 20° - 33\tan^2 20°+27)$$
$$=(\sec^2 20° -1)(\tan^4 20° - 33\tan^2 20° + 27)$$

Please help me to continue from here..