tan10度tan20度+tan20度tan60度+tan60度tan10度
=tan10(tan20+tan60)+tan20tan60
=tan10tan80(1-tan20tan60)+tan20tan60
=(1-tan20tan60)+tan20tan60
=1
tan10度tan20度+tan20度tan60度+tan60度tan10度
=tan10(tan20+tan60)+tan20tan60
=tan10tan80(1-tan20tan60)+tan20tan60
=(1-tan20tan60)+tan20tan60
=1