已知tana=2/5,tanb=3/7求tan(a - 知识问答

已知tana=2/5,tanb=3/7求tan(a+b),tan（a-b）.

1个回答

tan(a+b)
=(tana+tanb)/(1-tanatanb)
=(2/5+3/7)/(1-2/5*3/7)
=(14/35+15/35)/(1-6/35)
=(29/35)/(29/35)
=1
tan(a-b)
=(tana-tanb)/(1-tanatanb)
=(2/5-3/7)/(1+2/5*3/7)
=(14/35-15/35)/(1+6/35)
=(-1/35)/(41/35)
=-1/41

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