⇒ π/12 = 15° And π/6 = 30°

We have 15° + 30° = 45°

⇒ tan(15° + 30°) = tan 45°

We know that

⇒ tan15° + tan30° = 1 – tan15° tan30°

∴ tan15° + tan30° + tan15° tan30° = 1

Hence, proved.