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问题: tg70du tg50du-根号3*tg50du*tg70du

解答:

70+50=120
--->tg(70+50)=tg120
--->(tg70+tg50)/(1-tg70*tg500)=-根号3
--->tg70+tg50=-根号3+3^.3*tg70*tg50
--->tg70+tg50-3^.5*tg70*tg50=-根号3